High school takes up 3 months, Club takes up 9. Surely if Club is so much better than HS, the good will outweigh the bad. If most hs coaches are club coaches, that means they have to (or suppose to) be licensed. This makes it a more even playing field for hs.
The thing I like about high school is it allows communities to compete against each other and see who is best. You could make the same argument about club, but club is more selective and allows kids to come and play from other parts of the state. Club is directly reflected in the high school standings. Irmo (CUFC), Northwestern (Discoveries) and anyone else you want to add.
Also, I think you see club soccer helping schools who don't have a soccer program. Look at Midland Valley, they have a few kids who play for GA/SC Bulls. Midland Valley's soccer program was started for those players this year.
Hs can promote Club soccer. Look at Airport. A few years ago they had maybe 7 kids playing club and they were struggling in HS league. Now they have almost their whole roster playing and they are going to be competing for region/state. Their coach is a club coach and I'm sure he is promoting his club.
So no, I don't think HS soccer impedes the development of top players. Danny Cates was a national pool player and he carried DF his senior year.
