Kakashi choosing to only train Sasuke at this time was short-sighted and a waste of precious time. Gaara may be the most pressing problem now (at the time of this arc), but what about the team's future?

Kakashi doesn't know the full extent of the curse mark's effects or how long Orochimaru will remain an enemy lurking about, which means that for the time being, one must assume that Sasuke is in danger for an indefinite amount of time until Orochimaru is neutralized, which is something Kakashi cannot count on happening anytime soon.

Besides that, Sasuke's possession of the rare Sharingan makes Sasuke a target. Even if Orochimaru is dealt with, other hostile parties might be interested in a vulnerably young Uchiha who isn't much of a challenge just yet due to his youth and inexperience. Which means Sasuke has a fan-shaped target on his back.

If one member of Team 7 is a target, that concerns all of Team 7, not just on a personal level, but it's a matter of physical safety as well. If Sasuke is targeted, it is inevitable that Team 7 will get drawn into those conflicts as well, and they do, as the Forest of Death fiasco proved.

With that in mind, if Kakashi is truly interested in protecting Sasuke, he should be concerned with training his whole team so that they too can help protect Sasuke. Naruto and Sakura are going to be around Sasuke the most, and one can never be too prepared for an enemy attack. Sasuke might be relying on his two teammates to help him fight off stronger threats in the future, because three heads are better than one, and three strong genin stand a way better chance against higher-level threats than one strong genin will. After all, that is the entire reason for the concept of teamwork.

It was short-sighted of Kakashi to not consider how the team's overall improvement and growth in strength would contribute to Sasuke's protection in the long-term.