Your solution to increasing a player's ability is to reduce the amount of time they are playing which reduces their time on the ball and time learning how to play.
The player's already won't be playing 80 mins (except for the keeper) since any good coach and club will ensure there is even rotation. Team of 15 will have players playing about 54 minutes each game. Under this silly proposal they would go down to 40 mins per game. We won't even be producing players to increase the quality of 1st grade let alone players to make it higher.
Anyone who wants to further reduce game time has rocks in the head. The fact the 18s and reserves aren't 45 mins is a disgrace.