I've seen lots of posts on other parts of this site relating to improving the level of ability of our better players.
Limiting subs in HS play and club play would help. If you can name 7 and use 3 in every game, two things happen. First, players improve their stamina to be able to play a full 80/90 minutes.
Second, the 11 staters develop an understanding that becomes almost instinctive. Players know how their team mates think and play. When fully developed you can have players making passes to team mates without looking up, because they know that player will be there and is thinking just like him.
I also see that with multiple subs, players come in and out and often play in 2 or 3 different positions. Players should specialise, find their best position and concentrate all efforts at getting better in that position.
The point about blow out games is well taken. But the HS League can take that off the table by doing the sensible thing: have a mercy rule for soccer. If a team is up by 5 goals by half time, game over. If it goes into the second half, as soon as a 5 goal differential is reached, game over. I've seen teams come back from 3 down, but never 5.