For adversarial problems like this, a shadowban approach can sometimes be necessary. Perhaps people can still see their blogs but GoogleBot gets blocked from indexing them, or they only appear to someone with the spammer's cookies. That way it takes them longer to catch on and evade the model.
Of course, that means you'll need to at least spot check your bans because you can't rely on legit users escalating to you.
Of course, that means you'll need to at least spot check your bans because you can't rely on legit users escalating to you.