So, I played a certain multi-player game, which has a special feature that I like. It has a player behavior system similar to a credit score. The player can see their current "honorability" standing, using a number bracket as a basis, and their progression and rewards in respect to their standing. Highly rated players are usually teamed or put against each other in order to have quality gaming, minus the toxicity. Even though you don't get any honors from your team, you still get some ratings based on player's impact on the game (objectives taken, damage, kda, etc). Any misbehavior, players will see changes to their standing. And these deductions are based on player reports. A special formula is being used to calculate how much it is being deducted, but certainly frequent reports pull down the player rating significantly. Some of the punishments is longer queue time and less rewards to the player.
I think LOL needs to have special and seasonal rewards that is not attained through buying RP to good players (like something similar to a prestige badge, or skin), and can be taken away if they fall below a threshold. AND THIS REWARD SHOULD BE SOMETHING WORTH TO THE PLAYER! And the punishment system needs to be severe the first time around.