It's not that it's an "oversight", more so that auto battle doesn't necessarily translate to "the most efficient way to grind". As we discussed, auto battle doesn't field Protect/Potion/boosts, which means in situations where it would be advantageous to tank a hit with a potion (say, when Cure isn't in the current available loadout),auto battle will result in a death when it wasn't absolutely required.
And believe me, those wizards/gargoyles/spear-heartless can hit like a truck.