Very smart post, but THIS is flat out wrong. The best athletes do play these sports. Until MLS is economically viable compared to NFL, NBA and MLB, we won't see much of a difference in developing players.y.
I agree with everything else you said. The money issue is spot on. So I''m just going to focus on the area where we have a differing opinion.
So if our best athletes are playing in the NFL, NBA, and MLB, let me put it to you another way. Messi is not only the best soccer player right now but many put him up there with the all-time greatest players. But even though Messi is a word-class athlete, what would happen if he chose to play football, baseball, or basketball. With his height and modest jumping ability, you can pretty much rule out basketball. With his small stature would also rule out football. He doesn't exactly have the build for a superstar baseball player either.
So if the top soccer athlete in the world (Messi) wouldn't make a superstar football or basketball player even if he started young, why do we assume the best NFL and NBA stars would make world class soccer players? I'm sure there's some overlap and I'm sure we lose some good athletes who meet the soccer profile to other sports, but I don't think it's enough to cause the lack of skill, technique, and game I.Q. at our professional and USNMT levels. Heck, I could easily argue that our USMNT is physically superior to Spain's national team. Yedlin is faster than anyone on that squad and Jozy and Zardes are stronger and bigger than all of them. Yet we can't hold a candle to Spain in a competitive match. Also when Mexico kicked our ass in the CONCACAF Cup last year, it wasn't because we were athletically inferior in terms of size, speed, and strength. They simply outclassed us from a technical and tactical standpoint.
Soccer is a technical sport. Pure athleticism can only you get you so far without top class technical ability. And many times a player with high degree of technical ability with modest athleticism will do better than a player with high athleticism but modest technical ability. Football is different. If you're big, fast, and strong, and can hold onto a ball then that's pretty much all you need to be a top running back. Pure athleticism (eventually tactical awareness.) will you get you far.
US Soccer does not lack athletes. And it's not a lack of athleticism or coordination that is causing our USMNT to under-perform. We just have a very poor technical and tactical foundation and this traces to our lackluster youth development. Giving Lebron James a soccer ball at 8 years-old would just produce another Jozy Altidore 20 years later in our current system. And conversely if Messi grew up in Texas 15-20 years ago, he probably would have got cut from the team or put on a "B" squad due to his lack of height (He was '4'6" when he was 11 years old).
Like I said, I agree money is a problem. But it's not that more money will attract superior athletes to play soccer, instead more money will encourage more clubs and academies to develop superior soccer players. Once there's real money to be made, the US will start bringing in better coaches at the youth level and more attention will be made on individual development at the younger ages instead of pointless summer trophies for 8-12 year-olds. I'm sure this will also attract more athletes from other sports but the big difference is that we'll actually know what to do with those athletes because technical and tactical development will be a priority if they want to have any hope of developing a high earning player.