I can attest that smite and banishment and smite demon can all be rather effective against demons already. Holy Pyre is quite effective against the many varieties of undead and non-fire-resistant demons - I think it's interesting and appropriate that some demons are fire-resistant, including that fire-magic non-Holy spell. At most, like Arryn, I'd rename the spell before I'd make the damage from it more generic.
Just hire more 50-gold indy priests.
PvK