Seriously Reward For Good Behavior Already

There's already features implemented in ranked that work against players who disconnects and leave their team..

With that said, I agree with you about the "good behavior"-feature.

Allowing players to commend a fellow teammate, giving them a form of social score, could help the matchmaking system to pair well-behaving players with other like-minded, as well as the toxic players with other toxic players.

Almost like a soft-ban where cheaters, unknowingly, is placed in a game with only cheaters, the toxic players would be placed in a game with only the bottom-feeding toxic trash.