I kind of like a mixture of both. I usually pair up fighter and mage champions together. The spells that win me the day are usually haste and slow. My sovereign managed to beat the Burning Lands at quite a moderate attack/defense because I hasted her, slowed Dellin, and cast sticky mud in the middle of the battlefield and proceeded to skirmish him to death.
I kinda feel damage spells go from mana-inefficient and low damage to over-powered too fast. Also, if mages are meant to be viable in the early game, the robe that reduce tactical spell costs should be available in the shop mid to early game. I keep wishing I can find one among treasures for my spellcasters.
Also to note, Porcupine's crown is overpowered. 99% of my custom sovereign will start with it no matter whether they are spellslingers or fighters. Dropping regeneration, courage, flame blade without upkeep onto my sovereign at the start of the game is a bit too good to miss.