Maybe its time to blame the players and not the game. The matchmaking cannot predict if somebody randomly decides to throw a game or suddenly plays so bad that it looks like he would throw/troll games. Inconsistent player performance is the problem. Maybe there was a dude who played top lane to plat and read on the boards that ADC/support has way more influence and requires no skill/knowledge, so he proceeds to play botlane thinking that he could do so at plat level. But he has no clue about match ups and what to expect, because too lazy to actually learn first. Result: insane amount of mistakes and bad plays, no chance for the team.
Another issue is autofill, not autofill per se but players who can only play one role and refuse to learn other roles for the cases when they get filled.
And let's make this clear, you will get auto filled and you just have to deal with it. Period.
You have to learn all roles anyway, because you can't get teamwork if you don't understand how the other 4 work.
So maybe they dodge, which would then be the more reasonable decision if you absolutely can't play your assigned role, but then you also often get player that are like whatever I just play this and they are then essentially doing what I said first, randomly throwing games, because of refusal to learn.
Don't expect the matchmaking to fix that, it's the players and their attiude. Stop giving them excuses! They need to stop and learn their fucking roles!
The more team focused the game becomes the heavier this behaviour will impact games, because you just have to rely on decent team mates to some extent. Basically players that don't want to learn no longer have a place in League of Legend, they are toxic for the game. Incompetence destroys the game.