Penalties are not harsh enough for griefing
Everyone's probably tired of reading these but I gotta do it.
So I don't know what its like in higher ranks, but in bronze I find myself constantly being frustrated by players who have zero intention of playing the game and are just there to grief. Nothing is more annoying in a game mode that's supposed to have a competitive element than some random edge lord joining EITHER team and they just run down mid all day because they wanna throw a "Pity Me" party.
This has NOTHING to do with performance, I would rather have my whole team off meta and go 0/30 than get matched with one of these people. Otherwise, whats the point of ranked? If I have to stay in Bronze for the rest of my life because i'm not good enough for silver, so be it, but with how many griefers are running around its getting to the point I don't even wanna play, and this game is pretty fun so its my last option.
The reason I bring up other ranks is because this has not only happened once or twice, its consistently the case where in the lobby i'm praying the first thing out of my teammates keyboard isn't "Trying to reach Iron 4" then they proceed to ban a teammates selected champ.
I can totally understand this is probably a difficult thing for Riot to have to deal with, but you have your lower ranked players who are PISSED because they cant even go to the competitive game mode of their favorite game and have it be competitive, in Diamond I imagine players hope for a good teammate, in Bronze, you just hope for ANY teammate who will play the game.
TL;DR - Dodging isn't a long term solution to griefing.