Or a river.
I would suggest far more people have tried swimming than have ever played basketball, dominated by the creators the US of A. I would bet Jordan, his wife, his kids, his siblings, his cousins can all swim. Starvin' Marvin has probably not learnt to swim, and probably has never seen a Basketball court..
For Usain to be anywhere near Phelps, he should have done the 100, 200, 400, Long Jump, 110 hurdles and 400m hurdles. But he stuck to flat sprints and short distance, his swimming equivalent would be Pieter van Hoogenband or Alexander Popov. Phelps has no track equivalent.
We will never know how Bradman would have gone against the mighty Windies teams, but blokes in his era have comparable averages to players these days...except of course for the Don.
As I said, no issue with the Fed, I just think golf is harder