Decreasing the amount of varsity players will have only one effect in high school: less interest in the sport.
High school is only four years long. Not much time to practice to get to the top 6 in the school. If any kid knows that much, he/she will never join tennis because he/she knows that they will never get to play.
No one in high school cares about the quality of a tennis match. The average student passing by can't always tell what is a good match and what isn't. If they can't play, they won't bother to sign up or try out. The fact that there are 12 varsity slots creates more interest, because there are more opportunities to play at all.
I am an unpredictable player. Even I surprise myself with some of the shots I make.