I've been a Black Widow fan since Iron Man 2. Despite a relative lack of meaningful screen time and no solo movies until Black Widow set to be released on May 1, 2020 I've always connected to the character.
Initially my outrage at Endgame was just because they killed off what was thought to be one of two safe characters (Nat and Clint due to then rumors of a movie and solo series respectively) and my favorite but months later I've had time to properly think on my issues and of course it's a deeper problem than the 'you killed my favorite character' arguement.

The Russo's and Markus&McFeeley have explicitly stated they didn't know anything about the Black Widow movie when they were making Infinity War/Endgame. No shit dumbasses. They've pointed to a nameless female colleague who encouraged them to kill Natasha rather than Clint (a version of the script had Clint dying) and with what that woman said "don't take this away from her" - I completely agree with. The Avengers (old and new) are the only family she has ever known, and despite all evidence to the contrary Natasha believes she will never be free of the red in her ledger and she sees this as her path to redemption to fix what she sees as her greatest failure - losing to Thanos and to make up for all of the terrible things she's done in her past. But the thing that really gets me is the fact that Natasha doesnt know her own parents names. Granted I take issue with the decision to make her "daughter of Ivan" because in the comics (and likely the MCU) Ivan Petrovitch is the man who brought her to the Red Room - he is NOT her father nor should he be considered her father. I'd have preferred they follow Russian naming conventions which would make her fathers name Alian (her middle name is Alianovna) or my own personal headcanon based off a few scenes from Winter Soldier that imply Nick Fury is the closest thing Natasha has to a father figure. That aside; she doesn't know her parents names, she was brought up to be an assassin in the Red Room so of course she would do everything in her power to make sure Clint's kids get to grow up with their father (add this to the fact they reference in the film that Clint once gave Natasha a second chance and this was her giving him one). Then goes the band of morons saying Natasha had to die because Clint has a family only to kill Tony - who also has a wife and daughter you idiots - later in the movie.
Then comes the part that really gets my blood boiling, they filmed that long extended funeral for Tony where all of the superheroes are in attendance and Pepper lays a wreath in the water. Then they release a deleted scene of all of the heroes taking a knee to mourn Tony on the battlefield. Does Natasha get a funeral? No. Does anyone even care that she died? Barely. Thor has a fleeting mental breakdown, Clint screams one line at Thor, Bruce throws a bench and Steve cries a single tear. Then they add a couple of throwaway lines about how Bruce and Steve miss her and Clint wishes he could tell her they won. There's no reaction from Okoye, the real Nebula, Rocket, Rhodey or Carol - all of whom have been working with her for five years and are presumably her friends. Not to mention Sam who the Russo's have stated is like family to her. And Tony has the most nonchalant reaction asking if she had a family? Yes, asshole you should know it was you! (I have a whole post planned for Steve but this is one of the few and far between moments where I actually recognized his character telling Tony they were Natasha's family).

Back to my point of the insulting lack of a funeral (bench throwing doesn't count). M&M have stated she doesn't get a funeral because she wouldn't have wanted one because she's a "cypher" and Tony gets a funeral becUse he was this well known public persona. In what way was Tony's funeral public? It's mostly just superheroes and a couple of family members of said superheroes. How hard would it have been to let Clint lay a wreath out for her? Huh?! It literally wouldn't have changed the runtime. The Russo's have said publicly that Natasha isn't as focused on because she's got a movie coming out - guess what dumbasses, it's a PREQUEL that has to fix your mistakes! They publicly admitted they didn't know anything about that movie and instead chose to unfairly shunt responsibly to the team working on Black Widow.

Another thing; there's this thing called character arcs. For the sake of comparison let's use the two major deaths of the movie, Tony and Nat.
Both of them are results of long-held storytelling stereotypes. Oddly Tony's detaj plays into a TV stereotype in which the hero expresses the desire to get married and/or have kids and promptly gets killed off. Natasha falls into the much more harmful, offensive and outdated stereotype of barren/childless women are inherently less valuable than their fertile counterparts and/or male heroes. Basically because she can't have (or just doesn't have) kids and he has a family, she is more expendable than he is. I went into Emdgame knowing Tony was going to die, his story arc was complete, there was nowhere left for his character to grow. He went from selfish playboy, billionaire, philanthropist to selfless hero and he lived a life that was admittedly cut short it at least he got to live his life.
The same can be said for Clint or at least nobody seems to know what to do with him besides repeated trying and failing ro retire and the fact of the matter is the second Joss Whedon gave him a family in Age of Ultron - the character ran out of story potential with the exception of passing on the mantle (the purpose of his Disney+ show) but even that pitch doesn't actually require Clint Barton.
Natasha by comparison has mostly been used to prop up the male characters she is connected to whether that be Bruce, Clint or even Steve. Granted that's a lot better than one dimensional sex object for Tony to lust after in Iron Man 2 but Endgame is where Scarlett is finally allowed to really act and do something with Natasha's character arc and her entire purpose is to die so the men feel sad (another thing that M&M have actually said). She was running the Avengers long after everyone else had given up, there was so much more Marvel could have done with her character especially given none of the Avengers characters left for the next team up film have shown any leadership potential - it should have been Natasha.

It's hard for me to believe the team behind Endgame is also the team behind The Winter Soldier becaue Natahsa was an actual character with a storyline in the movie - and was actually treated repsectfully as a character but alas now we have to hope Cate Shortland, Scarlett Johansson and the team working on Black Widow can deliver the Black widow film the character has long deserved.
It's odd to me that Marvel would kill off Natasha and then making a prequel about her - seems like they've shot themselves in the foot in terms of how much money the film will make. Kevin Feige seems smarter than that so I hope the rumors are true that Natasha will eventually be resurrected back into the main timeline. I'm excited but apprehensive about the Black Widow movie - Yay! Nat's finally getting. Her own solo movie but I don't like the idea of Yelena potentially getting Scarletr's other two movies - she should get to finish her trilogy just like all of the other leads. I'm not hating on Florence, I'm sure she's going to be a great Yelena but I'm just not ready to replace Natasha.

I'm sure I have more thoughts on Natasha in Endgame but this is all for now.