You obviously didn't take the time to build your spellcasters correctly. I went through with 2 bishops, bard, gadgeteer, valkyrie and ranger. My bard and gadgeteer were my primary healers later on because I didn't want to waste my bishops' spellcasting on buffing. The bishops ended up with the highest number of kills and that was without ANY 7th level spells.
My favorites were Whipping Rocks/Quicksand/Crush, Whirlwind/Toxic Cloud/Silence/Pandemonium, Blizzard/Iceball/Freeze All/Holy Water, Fireball/Firestorm/Boiling Blood, Turncoat/Ego Whip/Psionic Blast and Eye for an Eye/Banish/Guardian Angel.
Between those two and the 'spells' my bard and gadgeteer could cast with their special items, magic made my endgame a lot easier. I normally took out as many opponents as possible with magic in the first two rounds while my non-magic people used their slings/bows on them and then I'd take the group up to melee range to wipe out anyone left.
The moral is: don't underestimate the value of a good magic-wielding character.
