I simply don't believe this. There are enough great athletes to go around. Look at the Olympics -- US does very well, even with the diversion of pro football, baseball, basketball. Look at wrestling: we have a great development culture and thus compete at an elite level. No such structure exists for soccer. Belgian individual skills and game flow was just much more developed than the US.
I'm not sure the Olympics are a great example since a large number of Olympic sports are individual sports. It's easier to be competitive when you're competing for a score or a time versus being in direct competition with other teams.
You're both sorta contributing to the same point, IMO. Like you said, we lack structure. Aditionally, we also lack the interested bodies so competitive teams can play other competitive teams.
At any time, London may have 7 or so teams in the premier league. You have thousands of kids wanting to be a part of that with the facilities and coaching nearby to make it happen. That's a high concentration of talent and structure in one small geographic area.
Compare that to the US, where you have different youth organizations (ECNL, ECRL, MLS Next, GA, ODP, National 1 League, etc) and tons of individual clubs proclaiming to be the best league or best club to get money from parents. It waters down the talent pool and you never get the best teams playing each other on a consistent basis. We never see iron sharpening iron because our talent is spread out and there is not the structure to pull it together.