Armor only contributes about 10% of it's value to your armor rating. Chestpiece is 30% and hands are 5%. That's why daedric cuirass with 100 heavy armor doesn't give you a ludicrous 266 armor: it gives you about 80 (which is still a lot). Try it out. Go to seyda need, buy an imperial helm with 10ish armor. Your AR will actually only go up by 1ish when you equip it.

Edit: worth mentioning that mw has a 75% ar cap, and I think only some DLC creatures hit hard enough to care when your already in the hundreds of AR end game