I think most people have one defense stat, and armor items just increase it. I find this problematic though: if you're stunned, or paralyzed, or in some kind of state where you can't move, your defense should drop to 1 and you should be vulnerable. Likewise, certain skills (for example "Backstab") might be designed to bypass your defenses. However, armor should be protecting you from damage even if you're stunned, paralyzed, or stabbed in the back.
By the same token, a bludgeoning attack might be good for mitigating the effects of your target's armor, but it shouldn't mitigate the effects of a highly skilled warrior is going to be skillfully defend your big-ass sledgehammer bludgeoning attack.
So, it seems to me like "defense" and "armor" should be two distinct things. Right now I have Armor as simply a percentage reduction in physical damage. Am I overcomplicating things too much? Wondering if anyone else has thought about this same issue, and how they've handled it.