Because the creatures matching the imp and lemure are the lantern and hound archons. And those are as uninspiring as the imp and lemure.
To which I was originally inclined to say, "tough nookie" to, but if he's gonna blow all the money and time to research a spell, I figured I'd take a look at how to balance the valiance.
There is a specific reason for the valiance form in particular, *ahemwishfulthinkingoncollinspartahem*, and the fiendform spell just gave him the idea.
Side note: You'll note polymorph self/other does not allow changing form into outsiders, constructs, undead, or a few other things.
Side note 2: My suggestions are both Su and Ex. Nixing Su and Ex abilities but giving Sp abilities save Holy Word sound doable. If that kills it, I'm sorry.
Spell like abilities were not included because when I posted, they weren't included and I didn't want to cloud the issue of whether the current version was balanced.
I'll go grab them for ya.
Side note 3: DR is supernatural, so it'd be gone. SR is extraordinary so it'd be gone.