And I've already searched through this thread for discussion on fiends, but I still want to ask: What is the point of this unit supposed to be?
For example you could include a keeper instead that will actually generate depravity points, doesn't have the -1 to enemy wizards' casting aura but instead does unbind and cast two spells a turn including the excellent Song of Secrets and Progeny of Damnation spells and the realm spells, isn't exactly a slouch with its own damage output, has a 4+ save to the fiends' 5+ which somewhat makes up for the fiends' defensive bonuses (saying that, the fiends' defense bonuses are very good against units that want to roll 6+ to hit or wound in melee). On top of that the keeper costs 60 points less than the unit size for the fiends' bonus which could be the difference between being able to include something else or not. And both fiends and keepers are expensive non-battleline units, so you could say they are competing for points and thus the comparison is valid, it's not like you can slap in as many of both as you want.
I would want to include them, but it seems very hard to justify because of their anti-synergistic role with the rest of the army, being built for exactly what you don't want a non-HERO unit like them to be doing. Does this unit need to be fixed in an update? or is there a role for them that I'm missing to see, as I desperately want the case to be? (perhaps it's the "good against units that want to roll 6+ in melee" thing? anything!)