[..]
The need to define socialised gender based characteristics out of individualism and sexual preference seems an awful lot like an illexplained attempt to counter sexism. [..]
It seems more like accuracy to me. It's always been the case that the two things are different and while gender changes often from time to time and from place to place, sex doesn't.
Random example - in a typical hunter-gatherer tribe, hunting was done by men and gathering was done (or at least primarily done) by women. That's
not sexed. A woman can hunt. A man can gather plants. So those activities aren't sexed. They were
associated with a sex, i.e. they were gendered. For good reasons in that case, but that's a different topic. The point is that those roles are gendered and not sexed. That distinction has always existed, regardless of the language used.
Pretending that sex and gender are the same thing is part of the problem, not the solution. It's what leads to things such as trans activists telling girls who are into cars that they're boys. If sex and gender were the same thing, they'd be right to do so. More boys than girls are into cars (at least here and now), so an interest in cars is gendered masculine to some extent. If sex and gender are the same thing, that means that anyone interested in cars is male. But sex and gender very much aren't the same thing. It doesn't matter what you call the two different things. Sex and gender, bibble and flartibort, whatever. The fact remains that they're different things.