I'm not talking about fringe cases or the occasional dc. I'm talking about obvious AFKs that run against walls, sexists and people that feel the need to write "Idiot" in round 1 of every game.

It may sound harsh, but are people really incentivised to change for the better in this game? Chat bans are no threat and permabans are a nuclear option (also easy to notice). Therefore I think, it would be better to introduce a gradual punishment. Something that hurts those more, that hurt others more. Rating and accounting for player-behaviour would increase matchmaking times, but that's a trade I'd do any day. I can wait 5 minutes to find a game, if that leads to having better games. Because I'm not launching this game just to be stuck for an hour in a hopeless 5v4.

If you intentionally throw games away, you should enjoy others throwing your games too - so that you can recognize, that if everyone would be burning things down - the world would be hell.