I happily grant much of what you’re saying; I think the difference here in my view is that you can define groups in one way, and find that _other things_ can be predicted. No one said, “we will define African Americans by whether or not they have problems with high sodium causing heart issues” and then determined that African Americans have this medical problem. Race is certainly a suboptimal way to predict this medical problem; much better to have statistically determined genetic markers, or better yet, a complete rendering of the mechanisms of action. But we don’t.

I’m all for “variation with groups is larger than variation between groups”, both as a literal reality and also as a practical answer to the question of how do I go through the world without being a jerk to people.

Racial categories are squishy and permeable. So are ideas of species, sub species. They’re useful tools with sharp limitations. Again, some people certainly oversell the utility of the tools, often for malign ends. But it doesn’t mean it’s an entirely bankrupt view