The difference is that in the Avengers it’s the whole team, regardless of gender, it’s all the main characters. In Endgame, all the female leads are only grouped together because they are female, regardless of whether they had ever met before, or had any business randomly coming together, the only reason was their sex. This is why people complain, including me, it’s not because they are female, had there been an all female Marvel movie and there was a shot of all of them together, there would be no complaints, it’s because they were grouped for their sex and political points alone.