Pretty much so. Spacebattles does have more than one thread for vtubers stuff, but then again that forum has too much threads to begin with.
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(imagine actually have so much care about lore that you have a discussion thread for it)
TVA is practically the only one which is vtuber-centric forum from the get go. Any other example searchable via google is just threads on an existing forum for something else (GiantBomb, Tvtropes, that OSU game, etc).
Not sure. I do remember that at some point most of the folks ended up moving to that poast place and the guy from Varis forum thingie approached everyone there (I also got it, but lost the DM) to shill his forum, the one that cute and funny thing that is a red flag to people like us.