I'm sure the best athletes in America end up in the NFL or NBA. That's a decent pool (the American population) over 300 million.
But the best athletes in the rest of the world don't end up there. They go to Soccer, Rugby, Cricket, Tennis, whatever random local sport is played (Australian Rules Football...hell, table tennis if that's all you got).
If some dude with amazing genetics is born in China, New Zealand.... Fiji, whatever, they most likely ain't playin' NFL.... they'll gravitate towards their "local" sports, play them as a child, and so on. The best athletes really (however you define athlete, which is entirely subjective), could be anywhere, in any sport. I guess what we could say though, is that not all sports "bring out" genetic human potential like NFL, NBA, Rugby.
Just as an aside, and I'm not accusing you of this at all Dr.Bdan(!!!) but America is like a huge fish bowl when it comes to the NFL. People think it is ubiquitous or something.
Barely anyone outside of America watches the NFL EVER. I personally couldn't name a single player (current or historical), nor do I know any of the positions bar quarterback. Neither can/does anyone I know. What little I do know mostly comes from Hollywood movies, for example, the trope that the most desirable guy in highschool plays "quarterback".... whatever that means...
Likewise, I am sure NO ONE in America knows anything about Cricket. But guess what? The Superbowl only had 112 million viewers....
...a crappy "group stage" match in the cricket world cup (India vs. Pakistan) just had 1.5 BILLION viewers.... just a group stage game!