I personally really enjoy the whole Mega Satan progression. At the moment it feels pretty rare, to me any way, to get an Angel room with an item, let alone a good item. On the other hand though this might make people view Angel rooms as worse than they already are, but really its just a case of buffing the chances of an actual item to spawn in an Angel room. Or keep it like the current Angel room fights where its entirely optional if you want to pick up the items before the fight, or at all, and you just have to avoid them during the fight. Make it so that the items, if you got items in the room, would be unavailable for pick up whilst fighting a Dark Angel so that you can't accidentally give up any health during the fight. Why not make Devil Rooms have Dark Angel statues, instead of the normal Devil statue, that you can also bomb and fight for the key pieces?
We have Dark versions of the Angels, yet they only appear in the Mega Satan fight. I don't think its an Angel Room issue, but a Key Piece issue.