Darkpromise armor bonus too low?

[gisborne]

I've been looking at the Darkpromise set for my healers and noticed that it has a 312 armor bonus instead of wounds or some other stat. I wouldn't mind this that much (on WP at least, it seems useless on cloth healer) if it weren't abnormally low. Shouldn't it be giving the equivalent of 78 stat points in armor? Based on talismans, each stat point gives 5.5 armor, so the set should give 429 armor. Additionally, the Redeye set, which is 3 tiers lower, gives a 528 armor bonus.