I feel like Day[9] (the former starcraft procaster - he does hearthstone streams mostly now) has a pretty good handle on his massive community, but I know they have a ton of moderation set up and the twitch chat is stratified during shows so if you run your mouth and get banned you wasted $5. Also does a good job emphasizing community-beneficial behaviors and explaining to users how to move beyond petty arguments.
Idk I feel like good community management on a large scale is possible, it's just no one wants to put in the effort because it's a long-term investment with no clear fiscal return, even as everyone complains about 'such-and-such place is toxic and everyone hates it'.