I guess that at this point of the game development it is probably too late to change core mechanics like armor, but i feel that making it block 100% of the magic / physical damage AND makes you immune to CC makes it a bit hard to balance the game properly.
Sure, some enemies have some armor type that they are very vulnerable to, like physical damage to a lot of mages, or that heavy armor types usually have lower magic armor, something that balanced groups can take advantage of.
But it also means that situations happens where a character, usually the mage, will find himself in a position where he cannot contribute to anything in the fight. For example, if a rogue almost killed an enemy, with 5% hp and 100% magic armor remaining, but said mage's damage is all magical, so he cannot land the killing blow.
Sure, there are a couple of spells that allow you to deal physical damage, and some melee skills that deal magical damage, but whenever you use a wrong damage type, you feel like you wasted action points.
I would rather have the armor block something like 50% of the incoming damage, the other part of the damage being dealt directly to the health. Then, in opposition to pierce damage, you could introduce some skills that deal extra damage to armor or something.
Finally, I would bring back bodybuilding/will, and give a sizable bonus to your saves while your armor is still up.
Anyways, just I feel like the concept has so much untapped potential, and that the current iteration simply promotes all physical or all magical groups.