He actually exchanges a significant amount of efficiency in exchange for a significant amount of damage reduction. It may not be a bad deal, but it doesn't appear to be broken.
I would disagree. Since he's a standard build in everyway except for the weapon talent he's only ever 1 attack bonus behind. Being 1 attack bonus behind is only a 10% decrease in hitting if there was a 50% chance he'd hit in the first place (50% to 45% is a 10% decrease). If he has a 60% chance to hit, then its an 8.3% decrease in hitting (if its a 40% chance to hit to begin with its a12.5% decrease, but you're already in trouble anyway at that point), Thus if you have any situational bonuses (righteous brand, flanking, etc) the penalty is further mitigated away from the fearsom 10% less likely to hit.
Still, its a good enough estimate. So if you hit 10% less, that means if you were going to hit 10 times in one fight you will now only hit 9. In any given battle thats going to be difficult to detect how much of a difference it made, or even if it statistically happened, espeacially if you attack less that 20 or so times (assuming the ~50% to hit).
Even at higher levels this won't change much, you'll still have just 1 or two hits per battle that didn't connect because it was one point too low, and it will be have less of an impact on the battle then the fact that you've taken 30+ less damage. You'll stay alive longer, which means more you're in the fight longer, defendering people longer, keeping marks in place and possibly doing fun things like the auto 1W damage stances or something and not using up the healers resources on your poor damaged frame. Its not going to break the game that you took 30+ less damage, but it will have more of a beneficial impact than having a +1 to hit, or so it seems to me.
The accuracy doesn't seem like as significant a loss to an otherwise standard build, not in comparison to what they gain.