I honestly don't get the complaints about Brie Larson's performance. It seems to be quite divisive, with most praising her as a highlight and others saying she was probably the weakest link.
Personally, I feel like a lot of people who blame Brie Larson's performance probably just wouldn't be fans of the character in the first place - combine that with some people automatically dismissing her performance because of her "ideals" or whatever. However, I think that the talk that she's miscast will be thrown out the door completely when Endgame comes around.
As always, the more negative voices are going to be the loudest, and that goes the same for Brie Larson's performance. There's nothing wrong with her performance, she does what's asked of her in the script well and shines when her character shines.
Overall, I think the biggest missteps in the movie are what Movie Bob says about the lack of character building in some instances, although I loved that final confrontation with Yon Rogg, and how she stopped trying to live up to his expectations.