> What such a comparison would prove?
Prove? No, what can be learned. If you want to fix healthcare, you look at countries with working healthcare systems and see what you can copy. Same here.
And there's plenty of countries with black populations even outside Africa - the France and South Africa you mentioned, then there's also the UK, Sweden, half a million in Germany, a million in Spain, Jamaica, and I'm going to guess a large number of South American. 1.4 million in Mexico, 300 thousand in India (https://en.wikipedia.org/wiki/Siddi), and I'm sure I missed plenty.
It's the height of US exceptionalist hubris to think nothing can be learned from all these countries.