Few suggestions on improvements.
Mentality - a new attribute. If things go bad, a player with low mentality will be likely to tilt - play much worse throughout the rest of the game unless certain conditions are met (to de-tilt him) such as taking baron. A sports psychologist will prevent this from happening as much.
Injuries and random events which stop players competing for a temporary amount of time.
Player to coach. Players who retire/get old may turn into coaches, which allows a team to convert an older player into a coach for a set amount of money,