This is probably less true than you'd think. Freak athletes are great athletes no matter the sport.

There's kind of a soft cap on NFL player height at about 6'5" or 6'6" - hardly anybody is taller than that. But the NBA is majority guys 6'6" or taller. That split isn't because all those kids got sorted into the right sport when they were kids. It's because if you're enough of an athlete to go pro and tall enough to make a living off basketball, that's a lot easier life with a longer career than playing football.