Well I feel like Angels would make for great high level enemies & one thing people need to remeber is this is an RPG w/ porn so having enemies actually get tougher is kind of expected. If MC gets into conflict with the LoL then of course he will send his minions, including angels, to deal with MC. If players get to the mid-late game & havent done enough quests to at least hold there own then that's there fault really. Same with Master & Reanna wo are pretty dam powerful foes if you're not ready.
I dont feel Angels should appear in Cath/Baron story. It would feel more natural if they are mid-late game enemies for the main questline (if MC is fighting the Lord of Light that is). They would be his servants after all. Cath/Baron would focus on the Bandit Conspiracy arc.
I would imagine the lowest ranking Angel being more like Greater Demons, then they get worse as they get stronger. But the stronger the Angels the harder they would be to manifest & maintain on the mortal plain so perhaps the really powerful ones are summoned as bosses or met in the Supernatural World during big Main Story quests. They may not even be based on biblical Angels, instead being Lesser Angels, Greater Angels ect... but I kind of hope they are more like Malekim, Archangels, Cherubs, Ophanim, Seraphim & so on.
Not ALL Angels have to be super powers mini-bosses, but having some scary Angels show up would be kinda cool. Would love them to look like marble figures with feathered wings & halos (mabey like the ones in Bayonetta? They are cool)