I guess I don't get the hate/concern.
Every Marvel movie that has set up a new character has had that character "pre final form". They've been uncertain of their place in things, and not quite the people that they will become.
-Tony is a selfish warmongering arms dealer
-Thor is an entitled frat boy
-Steve Rogers is literally a physical failure, and even once he becomes captain america, isn't really challenged to become the captain we know and love until he has to face the prospect of dealing with another super soldier
-The Guardians of the Galaxy hate each other, and are all considered felons or war criminals through most of the film
-Scott Lang is a criminal that doesn't know how to make a living any other way
-Every supporting character without a movie gets introduced as a rougher version of what they are, and we see them grow and adapt over the course of a film or so
But Captain Marvel comes along as an origin story, and a woman that's had her memory wiped, personality altered, physical body modified, and been pressed into service as an alien FBI agent, who's now learning that so much of what she knows might be a lie, while struggling to rediscover who she even is (let alone what), must be ultra confident, clear headed, and certain of everything about who and what she is willing and able to do with herself from the get go. Sheesh.