Well, maybe you can explain why Hide Expertise got nerfed then?
What irritated me about that was that it appeared in its gloriously brutal form almost immediately after they nerfed Avengers' AC for the same damn reason. While I was playing an avenger.
It certainly would be nice if they, say, kept track of things like that, and didn't appear to keep changing their minds, or, more likely, not entirely thinking about it.
The problem isn't adding 2 to the guy with a low AC to get him to not-quite-so-low, it is when you have a HIGH AC light armor character, which is MUCH easier to build than you seem to think.
My quick modeling was taken into account at 28th level, between a paladin and an avenger, each using a generic +6 armor from PHB, with one feat each devoted to AC (Unarmored Agility vs Plate Specialization). The avenger started at an 18 in Dex or Int, and the paladin had a shield. The avenger then got a +2 shirt.
They both wound up at the same AC. Which, for an off-defender, I don't have a problem with, especially if they're off fighting something in the corner that's not being marked by the defender.
Now, a swordmage or warden who makes himself relatively unhittable might well engineer himself out of a job; if the monsters can't reliably hit him, there's no reason not to go after the other party members, even if they're marked.
Sorry, HANDS DOWN this item is borked, it screws with basic game balance on AC.
See, that's the thing. I don't think that's an issue. Looking back at my light AC characters (avenger and sorcerer*), they really didn't eat terribly many attacks on AC, and the frequency with which they did went down as we went up in level as things instead started to more often NEEM or blast or mesmerize us rather than hit us with a big tree trunk. And especially once you get into late paragon and epic, things start just raining aura damage, which ignores defenses entirely. Which really made me think that WotC hates melee types. But that's a rant for another day.
* - Caveat: As a pursuit avenger, I typically went and hounded the enemy artillery or lurkers, both of whom tend to ignore AC (...while not running away, damn them), and the sorcerer hid behind the meat shields and thus was mostly subject to neeming attacks anyway. So my experience might well be atypical.
Giving one of these to our early paragon monk, who already has done some decent AC stacking IIRC, just means he might get missed once more in a session. He already gets in trouble fairly frequently (something about charging in first while shrieking out DIE MAMMALS!), so a +1 to AC wouldn't really prevent that.
Now, personally, I can certainly see making it Rare, since that puts it even further into DM Fiat territory, and the Fellowship certainly reacted as if it were rare. I might also switch it to Paragon/Epic and +1/+2, but keep it unslotted. OTOH, that leaves it both weaker and more boring, so I'd add in a Daily (or, hell, an Encounter) ability to negate a crit and turn it into a normal hit, as that also mimics the item from the book.
Brad
