The fact that it's slight is what makes it seem oblivious.

I can see that angle but it's also in a background of suppression of male femininity.

Men who consciously and intentionally attempt to subvert gender norms seem like they generally have issues with subtlety

Subtlety isn't everything.

Either gender expression isn't always subtle. Why does it need to be?

Are you applying the same caution to women?

This is very different from 'all cultures across time have/had gender'-- what do you consider a 'decent size'?

Anything above the small village. Sure I'm theorising here. But that's as a I see it.

There could be natural traits in humans that only become visible above a certain size. I'm sure there are mental conditions that are hard to notice in very small populations but are recognisable in large populations. Trends become more obvious and established.