The only things I find useless are the bless (spell not punk rock skeleton) archers are trash after first few levels as even if there is only one royalist it seems they shoot them most every time, get nulified, and damage your front line.
the bless spell is the one thing that actually made me beat the game, when combined with succubus just 1-2 bless spells with succubus can literally win an entire flank
