I may get crucified for this like I did on the other forums.  Another issue that isn't spoken about or even eluded to most times is the fact that there is no difficulty correlation between quests of the same level from different updates.  Compare Vale to Web.  Mob HP values, AC, to Hit are all different.  The trogs in Coal Chamber imploded under a 3RB from my screaming/bleed repeater last life.  Hitting drow with a lit2 was like pissing on a forest fire.  In so much I had to run a WOP exclusively, but it still took 3-5 volleys to con drow out, and forget conning out the reavers.

With AC they've painted themselves in a corner.  They've neglected AC for so long that a ton of rebalancing is going to have to go into it.  Not just AC numbers, but mob +to hit.