The swimming issue goes back a long time before straightened hair, though. There is some cultural reason why black people are afraid of water. Where I used to live, people said it was because the beaches were once restricted to “Whites Only.”
A black woman told me it was because they fear water due to the historic memory of their ancestors being thrown overboard into shark infested waters during the slave trade. Not kidding
... is more of anthropometric genetics between the races.
If you take a typical 6' black guy, and a typical 6' white guy, the black guy is more likely going to have longer legs (inseam), which means a shorter torso.
While that ratio may be a benefit in running, it's more of a negative in swimming, performance-wise.
There are reasons ships and subs are designed the way they are.
There are always exceptions, of course.