I run cloak on my Dark Brute. I also have that thing built for +to hit and +accuracy. +to hit is way better. THe Stun and Fear Auras on Dark Armor is part of an intricate dance of damage mitigation.
On a normal armor discussion Defense > Resist > Heal.
Dark armor has no defense, and if you build it, no defense debuff resistance. Great resists that can be built across the board. But that puts it second tier, right? Wrong!
Dark Armor has non suppressing stealth. Unless you are fighting things like Rikti or Rularuu that see through stealth you pick your fights. You can eat hundreds of Longbow and never disturb their friends 20 feet away. That is damage mitigation.
Dark Armor has the Fear and Stun Auras. Combined with massive to hit debuffs on a Dark Dark and things (minions) that are in your fight zone are pretty screwed. Then the Bosses hit you, and your Tank armor. BaB hit you? Click the best heal in the game, up every few seconds.
If you are not planted in one shot Dark Armor comes roaring back. The Cloak of Fear is part of the magic making that possible.