This completely ignores the influence that flagship instances have.

People don't become Neo-Nazis without spending time among other Neo-Nazis listening to Neo-Nazi talking points. People don't become Tankies without spending time among other Tankies listening to Tankie talking points.

People are more likely than not to join the flagship instance than any of the smaller instances and significantly more likely than starting their own instance. Some of them will realize the kind of people they have found themselves surrounded by and leave. Many more won't - especially due to general ignorance about Tankies (see this entire thread and the absolutely bizarre common defense of Tankies not being equatable to Nazis when they absolutely are and have resulted in more deaths and suffering than the Nazis ever have or will.) The people who stick around might start thinking the Tankies make some good points. This is how you end up with more Tankies. More Tankies is always a bad thing just like having more Neo-Nazis is always a bad thing.

Most people have a good sense to not surround themselves with Neo-Nazis. That good sense appears to be missing when dealing with Tankies.