We're not really splitting our top athletes though because our lesser talent doesn't play football, it plays those other sports. Of the big sports, basketball preselects for height, something that soccer has never cared about. So, tall people will still play basketball just like everywhere else. We don't see many 6'9 athletes in Bundesliga, for example.
Baseball primarily draws from overseas, it hasn't spent much time or money drawing from the elite U.S. athlete pool, preferring cheaper international stars. Hockey doesn't really have a national athlete draw at all, its more regional. The other sports? Tennis, golf, volleyball, etc. are the landing zones for athletes who don't have the insane athleticism required to be successful in football, baseball, basketball.
Football is the sport for elite athletes in this country. It already draws the best athletes. Shifting football athletes over to soccer is shifting the top of our talent pool into soccer, not splitting them with the other sports. A better comparison would be thinking about what would happen if the soccer crowd in Germany suddenly decided to focus on tennis, tennis would suddenly get the best German athletes instead of the leftovers. Well, that's U.S. football and soccer. Soccer would get the best U.S. athletes, instead of the 2nd tier.