I don't know about cranks and conservative grifters, but it's definitely not a feature of the "gender critical" position which I thought Dawkins was broadly aligned with. That's more that "sex" is absolutely binary, with your "intersex people" being umambiguously classified through genetics, while "gender" is too vague and undefined a term to be useful for much of anything in the public sphere.

> Dawkins has come out and written some pseudo-scientific bullshit about there only being two sexes/genders, and that everyone fits nearly into one of them

It'd be surprising for Dawkins to make any kind of definitive statement about gender. I do think that your use of "sexes/genders" in that sentence is symptomatic of exactly the kind of conflation you're complaining about. "There are only two sexes" is a completely different statement from "there are only two genders", and far more defensible.