I don't think this means as much as you're putting weight into.
I think the fact that somebody like MJ or Tim Tebow could even get a try-out in a different profession sports really speaks to top level talent being fungible. Like just imagine somebody practices being a Doctor for 20+ years and then gets an interview to be a World Cup Referee. Sure, they might not succeed at the other sport but the fact they can still do it is I think proof of sports fungibility.
I think there is a more self selection process happening for athletes and sports. People with natural athletic inclinations try lots of sports young, they will do well in the ones they are most suited for, and begin taking that seriously.
https://en.wikipedia.org/wiki/List_of_multi-sport_athletes
The list for college and high school would be huge. There is such a thing as athletic skill, I’ve heard it called a kinesthetic gift. People with particularly good builds, strengths, speed, agility, etc. can train those attributes across several different disciplines. As you get higher and more elite you will eventually have to specialize. “Jocks” in high school frequently played multiple sports and many lettered in multiple as well.
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.
American men gotta find their own way to become a world class soccer player. There's no pipeline like there is for the big 4. It's harder for teammates to gel when some went through the ranks in Germany, some in England, some in Italy and have only a few weeks with a new coach to buy into the system.
America's biggest rivals also aren't very good. So while the best European and South American teams constantly have to play each other and fight for survival, the US has to play middling teams like Mexico and Canada and tiny Central American and island nations.
He also runs a 4.6-second 40 meter dash, well fast enough for the NFL combine.