That's honestly not that bad of a monthly assuming there is a strong retention rate. It should also be mentioned that OF is not their only source of income. As long as they can keep the costs of producing more Youtube content somewhat in check, divert those viewers to either Patreon or OnlyFans and have decent retention on the outlets with high revenues per user (meaning, OnlyFans) they'd honestly be doing pretty well.
It should also be mentioned that some people were skeptical that they would create new OnlyFans content as opposed to just getting what they could off of the leaked videos. That's one promise kept, thus far.