The only time I see this inconsistency of writing both in original and Nick version is Musa's flawed characteristic be constantly tossed out the window.

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I get it people, people like singers like Musa because they're bold and rebellious but did you know in several instances Musa acts like Taylor Swift does in one of her songs. Another Picture To Burn is one of my favorite classic Taylor Swift Revenge songs about one of the boyfriends she had but unlike Musa she gives us a truthful reason why her boyfriend was such a jerk as never letting her drive his pickup truck that would have built up trust in each other. Whereas Musa instead of blaming herself she piles all the blame on Riven which is what people of captives and slaves have done throughout real history. What we get from Musa is truth from the writers she doesn't want to acknowledge how flawed she is she wants to stay living in her perfect ideal world with Riven being so far perfectly unrealistic and in Season 4 her music career goes to her head as well as her fame.
I'm actually glad in World of Winx Matt thinks Musa's bad at songs because she needs more dissonance for a strong reality check from honest people, Skylights. She thinks she's so perfect and can do no wrong when she's already been doing wrong since the reaction to the decent hat compliment in the Wildlands Episode in Season 2.
What else could Riven possibly say about that hat then it looks warm and it looks cool on her!? The third option Riven doesn't say because he doesn't like the word "pretty" and he doesn't like being mushy in public which are totally fine characteristics for him to have. Musa's expectations are way too high for him.

Musa's problem is she refuses to agree with anyone, Season 1 this problem is hinted at when Tecna says she shouldn't be complaining about dating a guy who hasn't asked her out nor even complimented her. Musa never listens to Tecna until Season 6 about the music thing. Tecna is a true friend despite not always understanding the emotional value of conversation she does recognize challenging her teammates to talk through things with others is a necessity with others. Tecna is the one who convinced Bloom to come with her to Red Fountain to talk to Sky and it is she who becomes the catalyst for encouraging Bloom to talk to Sky in later Seasons after Season 2's over the phone very heated argument, it is Tecna that reminds Bloom who is she around Sky and Flora who she is around Helia when they are both present with them. It is Tecna who reminds them both of what they taught her. "That a heart to heart conversation always helps" but in majority of movie romances we just get miscommunication breakup tropes consistently over and over again because writers are too afraid of revealing the truth which is actually why I do appreciate what Nick wrote for Musa in Season 4 they seriously heightened her biggest flaw caused from her Passive Aggressive Attitude of character instead of perfecting it they actually reveal the truth of what is really behind the toxicity of the relationship, Skylights.
Musa talks back to Faragonda in Season 2 complains about how and why she can't go on the Mission to Rescue the Pixies. It's a very whiny attitude and it is also quite steamy even more steamy than Stella who you can also tell makes sure people know she's aware that she's mad. Musa is never aware of her anger in all of her clashes with Riven in Season 2 when he never did anything too wrong.
Without Nick's Heightening this flaw of Musa's towards Riven and her friends and even one of her elders I would never have realized that Musa is actually wrong and I think the major reason they didn't let Musa sing any of most of the other songs is because she was totally not in the right mind set. And I don't think they wanted people to see singers turn into wnat Musa actually is she is a totally manipulative young lady towards Riven constantly taking over every conversation and constantly throwing the blame at him although Musa is not narcissistic her behavior is so similar to theirs. Instead of actually having a heart to heart conversation alone together she is quick to blame the faults he has already proven to let go of by Season 4. And twice in Season 4 when he is being exactly what a boyfriend should be, zealous and constructively complimenting her all she can give him is snarky backhanded compliments. In Season 4  episode Riven 1 Riven gives us his first compliment to Musa. "You look beautiful Musa." Riven says.
Then she replies instantly without even thinking about what she says about him to his face. "So do you, BUT it would be better if you were actually here!"

Musa as a Music fairy should known so much better because Music is instantly tied to the power of emotion. Musa is as much of anti-villain as Darcy is without being aware that she actually is.
Her "Heart of Stone" song is a Revenge song one again slamming all the blame on Riven yet while not blaming herself for her own mistakes towards him.

In episode 10 near the end of the Audition Riven constructively tells Musa as kindly as he is could. "Well, it's a miracle, you could have sung a lot better."
It is not an insult it is actually proper constructive complimenting and to top it off Riven was also encouraging her to reach her full potential but all Musa can see and her from his mouth in her point of view is misinterpreting them as insults that never happened.
And this leads us up to the point where Riven can't even let Musa see him crying and believe me a boyfriend or girlfriend you have to hide your tears from them when you're with them is not the right fit for anybody. Your partner should allow your emotions to show because there will be times when you can no longer hold it back and in anymore because they will need to see how much you've actually been hurt by them. Showing emotions allowing them to actually leak every once in a while is actually a healthy for couples and shows vulnerability and vulnerability is definitely powerful in some circumstances. In fact God intended us to do this is why we want partners we want someone like us who is also slightly vulnerable, empathetic and sympathetic those are real qualities of a true partner and they can be found in an couple if allowed to develop right at the right time, Skylights.
Nick fixed this plot hole that was left unexplained in Season 2 & 3 Musa expects Riven to answer to too many of her extreme high expectations that are just not possible for a human being to even answer it. And Rainbow messed it up again ignoring a vital character flaw from Musa that is from the original show.

Season 8 Star of Harmony completely contradicts how quickly one can overcome their flaws.

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The only time Musa doesn't back hand compliment Riven is when he fights on her behalf because of Nabu appearing suspicious in Season 3 to him which it is totally natural for Riven to be more suspicious of other guys tricking the girls like Musa because he knew that treachery because he fell into it and therefore he can really truly recognize it in other men so this is why he is occasionally grumpy around other men including when in confrontation with the Wizards of the Black Circle.

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This arc in Season 8 compared to what we've seen in multiple Seasons before is not Musa's natural character it is a redemption that comes too soon when her fellow companion of her official team and leader Bloom has three seasons plus a movie to finally stop using her aggressiveness on her boyfriend and her enemies. Musa's problem requires a longer separation and more dissonance on a really road blocked road to give her a reality check that she really desperately needs because her flaw is a whole deeper than the show makes it suddenly seem in Season 8 and is not fair to Bloom's character arc if you have multiple character arcs with personalities that will get a redemption arc the later redemption arc should take roughly the same amount of time that the previous character took to redeem themselves from their own flaws.

The Season 8 thing is flat and fake and rushed and disturbing to the eyes because of Musa not Riven even the episode where Riven is announced to be back Musa complains about him never calling her. Well duh you never called him in the first place he said in Season 6 he wanted to go no communication and it is confirmed by Musa in Season 7 that wasn't any secret sign of hers for wanting to call Riven, period. Season 7's Musa is excluded from the count of Seasons that have Musa's huge flaw.
Musa starts with this flaw in Season 2 not toward Riven but Headmistress Faragonda in episode 3.

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Winx Club Season 2 episode 11 Musa's even quite passive aggressive to her bonded pixie Tune not showing any sympathy that the pixie is under a homesickness story.

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Season 2 episode 18 really does show Musa's flaw as well as Season 4 of Winx Club Nick did.

Season 2 episode 20 Pixie Village she starts being awful to Riven.

So Musa's Passive Aggressive meets us head on in Season 2 is a constant theme and ties right into theme introduction by Wizgis that there will be opposing forces and also reenforces one of his first lessons in Season 1 in the episode Honor Above All Wizgis says a good fairy will always be challenged to grow on the inside as well as the outside the whole group was very honest in that episode with Stella being the only to slip into dishonesty on occasion up to Season 3's midpoint parts just to save face for the other girls when they broke the rules. Stella stops breaking the rules at Alfea after that season obviously tired of getting in trouble one too many times. It is also reinforcing what Wizgis says in Honor Above All "The path to becoming a good fairy is a long one."

Riven's talking back to Musa is him actually being a realistic and commenting constructively to the girls on how to get their mission moving forward but again Musa all she does is be immediately snarky to him for no apparent reason other than the excuse the reason that doesn't exist anymore.

Musa gives Riven very little respect when he has actually earned the other girls' respect. None of the other girls say or think he's saying something wrong not even Bloom who was the one who had the roughest confrontation with him in Season 1 out of all the girls including Stella. Stella and Riven were always on opposite sides of a spectrum her optimism and goofiness has always irritated Riven in Season 1. Stella was asking for his rudeness towards her she was behaving exactly like Amaryll towards the specialists he had every right to be mad at Stella and there for the case is the same in later Seasons he has every right to be made at Musa for how she treats him so harshly and badly and it is unforgivable that she won't stop blaming him for all their problems this is the opposite sentence to the Disney Princesses admitting in Ralp Breaks The Internet, "Do people assume all your problems got fixed because of a big strong man?!" This is a really big powerful one liner from Rapunzel the one line that saved her character face for me because in the movie of Tangled Rapunzel's voice acting was so weak especially when it came to the emotions compared to every other character in the movie including the antagonist outshone her in emotional voice acting. The face had the emotion but without proper voice acting the facial expressions mean very very little, Skylights.
Season 2 episode 21 below to check facts with what your brain might be making you misinterpret reality of a certain couple

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Season 3 episode 9 Musa displays more Rudeness to Riven when he just asked her simple question.

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Season 3 episode 19 was the Musa slapping the blame on Riven about the bike and constantly berating him about as they trained in its riding was wrong. Riven did actually answer her saying he did check it before they got going. And the result of her throwing the broken piece  is abrasive, insulting and embarrassing for Riven in his case which is why he refuses to show her his happiness at her Graduation ball because he is surrounded by everything he hates including Musa's blinded ego and stubborn passive aggressiveness.

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Musa doesn't know it but by calling Riven Crabby she tells us she is just as crabby as him but will never admit it, honestly.

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She does the same thing we see her do in Secrets of the Lost Kingdom in the Season 4 start in the above video about their relationship and The Magical Adventure movie which happens midway through Season 4.

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In the beginning seconds when we get Riven alone the animators bothered to draw and animate water flowing from his eyes showing he was just upset about Nabu's death as Aisha was yet when Musa comes up to him he refuses to show her his vulnerability and she doesn't ask him whether he is okay or not when he specifically back in Season 2 when Aisha, Stella and Bloom have already left he lets Musa cry on his shoulders when she really is worried about her friends. Musa has constantly been contradicting herself and lying to herself too. Riven doesn't get a thank you in this situation which would have been a good answer to his unusual behavior. The fact that Riven's tears are in the animation given Nabu being Riven's best friend cannon fact you can't unsee the tears the animators make it as obvious as Aisha's, Skylights which finally really does humanize Riven's growth in emotion this is the most emotional he has gotten in the show and therefore you cannot any longer say he's kept up being a jerk because he isn't a jerk anymore.

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At least Belle actually gives the Beast the words, "Thank you." for saving her life. At that point in time besides healing him it is the very least she could do. And boy is it is a strong thing for her to do showing that gratitude that gratitude