I can't speak to the others, but Twitch as a heuristic is going to be extremely misleading for WoW, since it's centered almost purely around the competitive asp

I can't speak to the others, but Twitch as a heuristic is going to be extremely misleading for WoW, since it's centered almost purely around the competitive aspects (raids and M+), and almost in sync with every other part of the game going to shit, those two have grown in popularity with proper "e-sports" style coverage being introduced. The WoW devs are still very good at making raid encounters and competitive dungeons. And they have literally zero competition in that area. So as long as they don't do anything catastrophic, they'll maintain that segment of the playerbase by default.