Naxx is 'our house' for aoe/pickups, not boss tanking(not that boss tanking is a problem)...now that we're GCD-limited to 96969, Exor is really not impressive for tank and spank...best case, I'd replace an ~850 damage JoV with a ~1400 damage exor, while possibly stumbling in my rotation, possibly having my judgement(typically the ONLY source of a melee slow applied) fall off if the next one misses...I do it sometimes on patch cause I can, but it's just not meaningful...hell, with threat the way it is, the raid is better off with me dropping sacred shields in place of cons/HoR after the boss is under control
PS
I don't mean that we're not a GREAT choice to tank Naxx, or QQing, just saying that our threat is almost unaffected by mob type, which is a very good thing indeed, because that lets Bliz balance us without a headache of making us either better or worse on undead/non-undead than other tanks that don't have type-specific abilites.
And, Exor/Holy Wrath are still awesome for other reasons- a second high threat ranged pickup on a short cooldown, which can be glyphed to interrupt...which I'm going back to sunday, 10% judgements= meaningless in 3.0.3 Naxx. if I needed OH GOD THREAT I can just exploit rank 1 ShoR and JoL
