Looks like KBin has an edge over Lemmy now in terms of monthly active users.
It's obviously a pretty silly thing, and is not in any way indicative of which project is "better" or more "long-term viable" or anything — instances of both federate with one another, and with the rest of fedi, so it's all one happy family.
That said, it's notable. KBin is a relative newcomer to the "Reddit-like fedi instance" game, and also does not have the tankie baggage.
Anyway, the more, the merrier!
KBin: https://the-federation.info/platform/184
Lemmy: https://the-federation.info/platform/73
Discussion on fedi: https://mstdn.social/@rysiek/110527049024028986
Regarding lemmy.ml as an instance: Dig further into it. They do have a certain ideology.
At any rate, you asked what evidence there is that the devs are tankies. I would simply point out that they describe themselves using exactly that word. And even the official docs are laden with political commentary. Regardless of what you think of their politics, or how much politics is "too much" or outside of your overton window, I don't think it should be controversial to call them tankies.
Thanks for the links, I will go exploring. And for the record I don't think it's controversial to call someone a tankie - as stated today is the first time I've heard the word.