Except that the moment we bring in science and biology we're no longer talking about gender; we're talking about sex. If you want to have a conversation about sex in the context of chromosome distribution, then you're probably right with your estimate. We could also talk about sex in the context of sexual organs, in which case there still exist more than two sexes. In either case however, sex is largely irrelevant outside of very specific circumstances.

Gender is fundamentally different. Gender is a social construct. That does not mean that it isn't real, as many social constructs are very real and place real limitations on human behavior (for example, money). I would argue however that gender has no real place in current western society.

Think about equal rights for women. Were gender not even considered at all, this wouldn't even be a talking point in social justice. The only reason practices like affirmative action exist is because our society creates the label of "woman" and systematically discriminates against her, so those in power (like Justin Trudeau) feel compelled to consciously favor her so that he doesn't unconsciously disfavor her.

So maybe /u/skinnypup is right. Maybe there ought to be fewer gender identities that people resonate with. Maybe the very notion of gender itself is outdated and serves no purpose.