I would say that Goddess could have been Isha/Gwen but we dont have any clue from her hinting that she's related to the cult, or the cult worships her. If that was the case it would not be MC to become the slave of Isha. Also we have very little knowlegde on Alaira, but if you're suggesting that werewolves derives from her ''natural'' powers thats a possibility.
Just like in Eyes Wide Shut, we have to change perspective. Up to a point MC only knows and thinks of Gwen being just a witch. Later we find that she herself is a Goddess. (that could also be a lie as she says she has nothing to do with lust of mankind, but all the corrupted women scream her name while sucking MC's dick
)
So when MC sees the cult event, he thinks that they've just spawned a demon infront of a naked women (at this point I'm kinda sure Chyos knows the true meaning of the movie) but maybe later on we will figure out that that women is not a demon or anything similiar. As she doesnt even resemble Syfa to begin with. Note: Syfa is truely a demon, doesnt wear armor, doesnt wield any weapon, much more of a succubus type magic and power shes got.
I could say that the cult is tied to Syfa but the original goal was not that. Marcus was trying to undermine the ''powers that be''.
I dont think the goals are changed, but the cult adopted some other motives. As they summon demons and control werevolves now.
Edit: I also have to add that I dont belive Gwen is Isha. So far she's only doing witch stuff. MCs dick got big, not because of her Goddess powers but a potion, as we also know any that drinks the potion the result is similiar (sabrina).
She sends us to hunt down some monsters? So she needs ingredients to be able to do ''Goddess'' stuff? Nah, she's just a witch.
Edit2 : On the other hand the only Godly power we witness so far is the power of Athia. Thanks to her power, Mira is the only girl that has resistance against MC's witch potion powered cum.