Buuuut, will be those orbs a dark conjuration? My guess is not
If cerberus will be a cool creature together with "terrain-conjurations", why putting him into FiF where will be no terrain conjurations?
Sleep, knockdown, teleport, tangelvine or stuck and he is a expensive 3 dice puppy again. If i want to protect something, i rather put a wall around it
I agree, that if we dont know the full range of new dark cards, we cant judge his efficiency on battlefield buuuuut defensive creature in Warlocks spellbook will be something rare in my area