The issue you're going to run into is PC AC versus mobs with incredibly high ATK. I'm actually arguing that AC doesn't make a lethal scenario come up that much less in the scenarios where you actually want gear. The shit you actually want some gear for in Velious is going to have really fuckin' high ATK.
Take a look at the AoW logs from beta:
http://www.project1999.com/forums/sh...d.php?t=150045
You have tanks who are presumably already at the softcap for AC getting smashed. Looking at the short logs, the DI (when you account for defensive) curve appears centered ~18-19ish.
If your non-defensive DI curve is centered around a DI of 18 with AC stacking vs a DI of 19 with HP stacking, it means fuck all if you're mitigating a bit better if you still have a large chance of being one-rounded.