it will just be even worse, a concentrated "tankie" circlejerk

It's already a tankie circle jerk over there, you can't concentrate what's already concentrated.

visible to plenty of newbies. Then what?

Visible yes, but its a LOT easier to say "Oh yea that's the tankie instance, they're small so just block it and move on" rather than

"Oh yea that's the tankie instance, but they're also one of the biggest instances, so if you block them you'll be cutting off a decent chunk of non-tankie content"

So many stories of "I signed up on .ml because it was one of the biggest, then I realized it was full of Tankies and signed up elsewhere" and if there's stories of that, there's probably many more where the person just left and never came back because what they saw was a place was full of toxic tankies