I hope the shrine god isn't malevolent. it would just be nice for her to have some access to an at least situationally benevolent supernatural force. just because its shrine doesn't exist in reality and mieruko and hana were likely pulled into it via the machinations of the shrine god, that doesn't mean that it's malevolent.
as to the idea that it makes a contract with spiritually powerful young women and then turns them into those shrine maiden ghosts, I don' think that fits; Mieruko is like a once in a generation spiritual talent from what we've seen, so that's probably not a sustainable source of maidens. I'm not even sure that there's more than just the two shrine maidens anyway, tbh; I think they just regenerate once they're destroyed because their existence is tied to the shrine god. and also, the shrine god only came out after the shrine maidens failed to kill the monster on their first attempt. if they had succeeded, the god probably wouldn't have revealed itself.
anyway, we've seen no evidence that the shrine god is malevolent in any way. it's kept to its side of the deal, it doesn't have the same gritty gory texture as the malevolent or corrupted ghosts, tho it also doesn't have the shiny glowy texture of the happy purified ghosts. It's probably something in its own category.