DRK needs a revision

[Brannigan]

Second, the counter attack was a signature ability, which was subsequently copied over to Shield Swipe. DRK lost the ability, and PLD kept it.

Paladin has had shield swipe as a counter from block since 2.0. They just moved it off the GCD later. Monk also had lolHaymaker off of evades. I'd hardly call this a signature ability of Dark Knight outside of the debuff it placed. You're better off talking about Low Blow and its reset trait for that, I think.
With that said, while I have a higher opinion of TBN than you (it basically looks good for dealing with stuff like tank busters, a7s lightning beams, and all sorts of other wacky single target stuff during progression), I do agree that Dark Mind is in a really weird place. I could see it being 30% without DA, and DA turning it into a group 10~15% or so. Cooldown is probably too short for that, though. Either that or give it some weird synergy effect with your team's spell casters (you gain MP when they cast? idk). Or they could have DADM max out the blood gauge when you take magic damage. Something like that.
Can't say I'm a fan of Delirium (design-wise that is, it might perform well) either. One of my big problems with DRK in 3.x was the boring combo paths since you never had to Power Slash. With the removal of Scourge and Delirium, DRK is basically a 2.0 paladin with Dark Fell Cleave and some extra oGCDs.
I think DRK will end up performing fine, but the gameplay changes are weird.