> Basically saying that women and men should present and behave within a narrow set of parameters.

I think you're putting words into peoples mouths there.

Acknowledging that there is a social construct we generally know of as "gender" and acknowledging that certain stereotypes and common understandings of that concept exist is not at all the same thing as demanding that people should fit into the narrowest stereotypes that you can think of.

Also worth noting that you acknowledging the existence of sexist stereotyping is an acknowledgement of the existence of gender as a social construct.

There are both descriptive and normative uses of gender. To use a less charged example, it's not prescriptive to identify as American. It's not prescriptive to say other people identify you that way, even if your passport says Canadian.

An example of using the category normatively would be saying someone isn't American because they burn the flag. My experience is that most of the people using "gender" normatively don't differentiate it from sex.