I played both DAO and DAI. I prefer DAI graphics but i much prefer the combat in DAO. I played DAI in nightmare difficulty and that game was.. more like an action game than RPG (combat-wise). Most enemies have inflated HP. Played as Knight Enchanter, and soo many immolate spam don't even nudge much of enemies HP. The real damage comes from fire mine? But kinda like the Knight Enchanter playstyle. You are actually a mage tank.
Anyway, i would prefer that magic to be actually powerful in RPG and tactical games. It feels "meaningless" and "stupid" that 100 fireballs can barely kill a bandit (that's exaggeration but you get the idea).