Of course pronouns cement regressive gender stereotypes. What do they think?!
When someone is introducing themself as she/her and is claiming it has nothing to do with their sex, what is it to do with?
And it must absolutely come from people who either want to inhabit those gender stereotypes or cement them in others. Otherwise it wouldn't have arisen.
For example, men who fetishise women, being called she/her, has a massive sexual reward.
Likewise people who claim to be non-binary. I don't doubt their motivation is to escape the gender stereotyping, but in doing so, they are cementing its existence. Far better to address its existence.
And as for gender fluidity which inhabits gender stereotypes on alternate days, depending on clothes...