Ah, is it because the spells are Arcane, and thus he can't use them in armor? Yes, that's right. So you're a non-primary caster who gets no special bonus to AC, and you're not going to be wearing armor. Or you're not going to be casting many spells. Wait, you won't be casting many spells anyway, because you get very few spells per day.
...Oh, and one more lovely feature: this class that can't cast in armor also lacks any of the basic armor spells. No mage armor, no shield. Good luck with that smite.