I do understand that it's problematic to ban accounts efficiently. Without having a person that checks on every report - unless it's for bad words - League can't know for sure the report is justified or not. But I do think that improvements are possible, even if it's not easy.
I usually send "specific" reports to Riot Support, with Screenshots. Like a Player taunting another player the whole game long to say something about him, as he will show him "what int really means", calling him names etc. I assumed he'd get a temp ban, let it be only 3 days, but nothing happened, his account was played on every following day, I've seen this multiple times. Which leads to my point.
**Chat Bans are worthless**
Yes, it's good to take out a flamer/rager by limiting his access to the chat, but he can still write. And one message is often enough to start the int/permanent surrender-votes whenever it's possible/going afk/following a target and stealing all he wants to get. My point is this doesn't help at all to fix the cause, only to temporarily fix the problem.
Players with any kind of misbehaviour should be removed from ranked games for a set amount of time - I don't mean years, just like a temporary ban. In this time the player has to proof with other gamemodes that he is "worth it", if he gets reported the weight of the report should be amplified to extend the temp-ban. Noone wants flamer/tilter/rager/afk/int in ANY game mode, but in Rankeds it hits especially hard.
**Why do I think this can work?**
I've seen it multiple times with a similar system, but had one specific experience. A friend of mine often left champ select/went afk ingame because she didn't want to play anymore or ordered something to eat and wanted to eat, like, this happened often...She didn't understand the problem with it. She got a Leaverbuster and had to wait 20 minutes prior to every queue for I think 20 games or so (don't nail me on the numbers). After that, it only happened ONCE in 7 months that she went afk because she got an emergency call. She had to "suffer" from the punishment, but wasn't excluded from playing the game.