I'll boil it down to this: Many, many people complain that the U.S. keeps producing big/fast/strong athlete-types, but our best club teams and national teams still cannot compete and are left chasing the ball all game against top sides from Europe. While I hear the occasional argument that "other countries don't have basketball and football to suck away the best athletes", in general I don't hear (nor do I feel myself) that our problem is a lack of athleticism. Rather, we don't seem to produce players that keep their opponents off balance (defenders are forced to give creative dribblers a few feet of space so they don't get beat), ability to keep possession in tighter spaces in the attacking third, and break down opposing defenses with creative dribbling and passing.
Why don't we produce players with these qualities? I am not about to claim that the absence of a U16 single age group is the root cause! But, our funnel favors players who are physically advanced earlier than others - because of how U.S. coaches look at things, those earlier physically developed players are better able to "survive" against players that are a year older at an age where a year can make a supersized difference. What is one thing that can help mitigate against this? A single-year age group that changes the focus from having grown enough early on to physically match up (which is a short-term factor) to a much wider variety of factors.
