You're so wrong. Mobs and players both use their attack against targets AC to determine mitigation. More AC = less damage taken. Now, the difference between 900 AC and 950 AC will be barely noticeable mitigation wise on most mobs, but 900 to 1000 or 1050 you'd start to see it.
The agility on this will also help with avoidance. Not to mention finding saves on gear for this level of player is hard to do as well.
Nice Under 40 armor, that can hold you over into Tae Ew or Links of Hardened Clay.