I think the concept of gender, as different to sex, was very useful to second wave feministsand the social sciences, when the idea that biology does not determine interests, personality, abilities etc. first took off.
When gender was used as a concept to e.g. point to gendered socialisation, on the basis of sex, this was quite extraordinary, in a world that considered womens role in society as a biological destiny.
But back then, it was obviously used to explain how gendered expectations were holding women back, as a class, and the whole point of the concept was that it characterised social phenomena, as specifically opposed to something innate.
Now that TRAs are turning it back into an innate property, while obviously completely overlooking the shittier, unpaid labour, aspects of womanhood, and using it to undermine the understanding of gender as a hierarchy and women as a class, it is arguably time to retire the concept.
Although, having said that, I think we do need a term to denote those social aspects that many people of one sex have in common, such as the sense of entitlement many men assume in many interactions, even when they are not aware of it. That is clearly not biologically but socially constructed, so it is useful to have a concept to apply to all those socialised aspects that follow having a particular kind of sexed body.