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You're completely missing one of the best parts of this. Granted you can't use it on heroics or bosses with adds, but if you are fighting a boss with no adds (of which there are plenty) you can use this as a tank cooldown. If you read the description, while you are channeling this spell you have a damage reduction of your dodge plus parry. Have 20% dodge and parry? While channeling you take 40% less damage. That's pretty much as good as a second IBF. Granted you can only use it every 10 minutes, and granted you generate no threat during the cast, but if you know how to use it right, it's a pretty cool spell.
As a CD, it is still fairly mediocre. While casting, it completely shuts down your Dodge/Parry. You just convert that into pure mitigation. Slightly better than avoidance? Yes. But not by a ton. And I'm not convinced it is worth 3 runes for such a small boost.
Now, if the boss uses some kind of spell that hits hard and you know when it's coming, sure--it's useful. Because your Dodge/Parry won't have* reduced that. But you need 3 runes, of all 3 types, to cast it. So you will not be able to use it without burning ERW/Blood Tap or you prep for it. Both mean lost threat, but prepping is worse since you will be constantly behind on your generation waiting for this to happen.
But this requires you to be REALLY quick, and for there to be a cast time/warning before it happens.
And, even then, it is a (say) 55-65% reduction on ONE hit the entire fight. And that hit will eliminate some ghouls from your cast, so you may not get any threat from it.
Gimmicky for the most part, occasionally useful in raids and/or Heroics.
But, like you said, it is good for soloing elites (like Chillmaw).
[EDIT]
*potentially
Edited, May 8th 2010 9:57pm by idiggory