Many of the top club/academy players don't show as well in high school because:
1) Their high school teammates are not talented.
2) They're forced into an unaccustomed role or position to meet the h.s. team's needs.
3) Their h.s. coach is not that good.
4) Any/all of the above.
Yes, (even talented) younger kids do benefit from playing vs. older ones in h.s. The best way to put it is this: A talented (club/academy) freshman benefits from playing/training with older kids. The benefit declines sophomore season. By junior and senior year, from a purely developmental perspective, playing h.s. soccer may actually be detrimental to an elite-level kid.
