I love my staff/dark brute to bits. Properly built out, dark is a beast of a defensive set. Between the resists, Dark Regen, and Soul Transfer, you're rarely hitting the hospital or asking for wakeys. That said, I also chose staff for her partially because Form of the Soul would help with the endurance issues during leveling. That also said, its not like there's plenty of other armor sets with endurance issues. Still, there's some room for improvement in DA, or at least discussion.
This right here. I don't call her 'Toggle Lass' for nothing. You have seven(!) toggles, two clickies, and zero auto powers. One of the toggles is also your damage aura, so that's even more endurance drain. The other damage aura sets get some endurance mitigation so you're feeling kind of left out here as well. I'm not sure I'd want to change any of these to auto powers, but I do feel that's something worth pointing out as to why everyone feels DA is hard on endurance.
Cloak of Fear improved when fear went from 'run away' to cower. Now tanks and brutes don't have to worry about chasing off the guys they want to taunt. I use it on my brute as cowering minions does give you a little bit of mitigation, and it makes a convenient set mule for Siphon Insight. I imagine it might be a little more useful if you buffed the to hit debuff, but I'm playing a brute so what is debuffing even.
Oppressive Gloom, meanwhile, is where DA really needs the rework. A mag 2 stun for an HP drain? Even if that might be useful mitigation for scraps and stalkers, they don't have the HP to actually use it. I don't know if Cipher can run the stats, but I'd easily believe this was skipped on like 99% of dark armor builds.
Alternatively for Cloak of Fear, I can endorse this. Playing a staff brute with no inherent +to hit outside of Form of the Mind levels, I weep every time the CoT drops my roll to hit down to below freezing. Being able to shrug off their attacks doesn't help when I'm flailing away helplessly back at them.