The real problem isn't the player, its how the system handles the player

A player can get banned all they want, they will just run to a new account (reformed or not) Riot has to actually work AT the problem itself if this company wants to see some real change. I listed a topic about implementing some ways (especially for long time players) to help Riot recognize the legitimacy of their efforts and they just ignored it. Instead of straight up banning players, why not actually work at building a system that actually keeps track of their behavior with like a "behavior" tab listing a graph of how many days a player has been positive and rewards them for it, so it actually helps stay changed, before its too late and you just end up losing everything. Which only results in anger and revenge most of the times.

Edit: you can remove something that stinks, but it will still stink. If you actually clean it, it can be worth something.