Reading this poll got Whitey thinking.
If fiends can't do so, how would they attract a following? Arcane spells like
planar binding and
contact plane would let a caster get some direct benefit - and run a serious risk too - without really needing to pick a particular archgoon. Evil type clerics are then shoehorned into a couple pairings of domains, and even moreso shoehorned into one evil deity's theology. Makes 'em get stale after a while.
Worst of all, that makes the big fiends just real big stats waiting for a munchkin PC squad to take a swipe.
Here's a possible solution. Demon princes/princesses, devil lordlings, and so on grant spells. But they aren't the 'battery' for them, so they don't need divine rank. Vaguely like the Devourer's spell deflection ability, they expend the life levels of those souls consigned to their plane. This gives them - particularly the CE bunch, a reason to traffic in those, and a compelling reason not to just
gate in and thrash the Prime. All that arithmetic keeps them busy. The intrigues of who gets to cast what and when makes a hierarchy of both fiends and followers important - something the party may or may not want to get tangled up in.
Sure, that's not in some splatbook, periodical, FAQ, or whatever. But it's got that D&D plausability. If someone wants to give it a try, it'd be keen to hear how it turns out.
And if someone is really sweating how fiends do their thing, just tell them they really don't want to know.
