Maybe a better option would be to limit the number of communities one can create (or become a mod of) in a limited amount of time? (e.g. you can create or be a mod of up to N communities in M hours/days) This would reduce the number of spam community creation cases and won't be over restrictive.

Also, anyone can spin up an instance and create any number of communities there, but I think that is a significantly different case than one creating 1000s of communities here. It requires more time spent by the spammer, and most likely some money, which would discourage at least some spammers.