This is something Riot Games has spoken on, the observation that ordinary participants can have a bad day here or there, and that forgiving corrections can preserve their participation while reducing future incidents.
Recently picked it up again and I noticed that I didn’t had to use /mute all anymore. I’ve got all-chat disabled by default so I’ve got no experience there, but overall I’d say it has come a long way.
But I’d also say it depends which mode and MMR you are in. I mostly play draft pick normals or ARAMs in which I both have a lot of games played - I heard from a mate that chat is unbearable in low level games.