Very interesting subject indeed. The way I have always looked at this and the reason I see a real benefit for some players to only play academy and not high school is that there is more soccer development momentum in the academy program. High school soccer is lots of fun for the kids and no one can discount that. The joy of competing in front of your peers week after week and enjoying the accolades in the lunch room cannot be matched by the academy experience. However, for players who are talented as the academy players generally are, the high school season for the most part is an interruption of a highly optimized training regimen that is neccessary for players to achieve their highest potential. There are a couple of reasons why this is so.
1. For high school soccer the, emphasis is on winning as opposed to development.
2. Since the academy players are generally more developed than their fellow high school players, the coach will not focus on their development needs in high school because they will have their hands full with other needy players.
3. The academy players will not be pushed in practice or in the majority of games to play at a high level because of a lack of skill in their team mates and in the opposition.

Yes we are lagging behind in soccer development when compared to europe. In europe once a kid is identified as having soccer potential, they are given a lot of structured assistance to develop that potential to its highest level. Indeed some kids drop off, that will always happen, but atleast they are given a chance to really focus their efforts on becoming a professional soccer player. For successful development, it is crucial that the soccer player masters a certain aspect of their development at each stage. By 13yrs of age, the soccer player should have sound technical skills for first touch, ball striking, passing and dribbling. By the time they are 17 they should have a good mastery of tactical play, positioning for different formations, moving, cutting off passing lanes. The successfully developed player will need so much time to master these skills at a high level. We know that these kids still need to be in school and get a good education. If they are to have any chance to compete with the international kids they need all the extra time to be focused on highly organized training.
High School soccer greatly interrupts the needed development process for academy players and significantly impacts their ability to maximize their full soccer potential by hindering sustained development.