Ironmouse is the most popular female streamer on Twitch (by subs). Pekora is in the top 5 most watched female streamers worldwide (by viewer-hours).

It’s not needed for guys apparently, but it’s not niche.

Do all subscribers to team subreddits follow the main sub as well though? Because I assume fans follow "their" teams' subreddit, and there's several in the 100k range.

I think most fans subscribe to the "main" sub (r/hocket, nba, baseball, etc) for general league news and discussion in addition to team subs.

Hololive functions in a similar way - the most popular members have their own subreddits in addition to the main hololive sub.

Yes but none of them are using voice changing that makes it hard to listen to. They all speak in their natural voices or with a natural manual affect that they prefer to put on, something that computers don't seem to be able to replicate yet.

I watch Japanese vtubers quite a lot and enjoy doing so, but I couldn't personally listen to Lina as the voice sounds grating on the ears.