Kav
yeah, except nobody cares about their mmr in casual, it's only used to balance teams to (in theory) make them more fun for everyone
when you have a publord scunt dropping ~50 frags and losing, and therefore losing mmr because the system weighs win/loss more heavily than individual performance, it just makes future matches for that player more unbalanced because the system is weighing team performance more than individual when considering individual skill level. and this is compounded by the fact that it's casual and most players probably aren't playing for the win anyway, they're playing to have fun, whether that's by going friendly heavy, or trolldier, or sniper, or spy, or whatever. in that kind of environment where win/loss doesn't matter to the players, why should it matter to the matchmaking system?
but to reiterate: valve doesn't care, and we probably shouldn't either, because it's fucking casual. i'd rather they spent as little effort on it as possible so that they can work on the real problems the game has: the ambassador being too good and pyro not having enough mobility