I disagree, I've seen some great DRKs tank stuff and they gear nowhere how you would have done it.
One of the major parts about them being able to hold hate is them being able to deal damage in order to maintain hate. A big part of the DRKs I've seen tank stuff is the fact that they have Apoc as well, which totally changes what the job can do.
Personally I think there's things they shouldn't attemp to tank, as some LS's fight mobs differently, my LS does not throw DD's at stuff as Khim/Tia so I think in that situation a DRK wouldn't be able to hold hate very well. For shit like Nid/Faf/Aspi/Cerb, mobs where we have no problems throwing melee at it,
I think they could do a great job as long as they could output good melee dmg.