Seems like the real issue with League is Riot's unwillingness to permaban players and enforce its rules

Agreed. It's possible to solve these problems, but Riot didn't care enough to solve them, or they had an underlying motivation to keep toxic players around. It does seem like a problem that's not unique to Riot, though. I think there are some structural issues in these games that makes it easy for companies to ignore the player experience in favor of just keeping people playing. It's probably similar to all the attention economy websites where they don't care if you're getting value, they only care that you're still on the platform.