I know I'm beating a dead horse here, but the elephant in the room needs to be addressed soon.
Living Dead is a liability, not a Cooldown.
People have said it time and again about how this skill throws healers for a loop unless you have a WHM, but back then both SCH and AST had the tools and abilities to overcome this liability in both a raid setting and in a dungeon setting.
Now, in a dungeon setting, DRK has to hope he gets a WHM or else he can't use Living Dead due to the new HP increases they forced on Tanks this expansion to adjust for their new design for Healers. Living Dead has been the only cooldown since inception to be detrimental in more ways than one, and if SCH/AST don't have their resources ready to allocate to Living Dead, the DRK will die.
Yet WHM has no issues with their plethora of healing tools and their ability to make someone go from 1 HP to 100% in a few seconds due to their "pure healer" design philosophy they've taken. If we're to balance this out so DRK isn't the Black Horse it already is, we need to find a solution.
Given DRK's current state, it would operate well in 8-man raids, but it lacks heavily in physical defensive CDs compared to the other 3 Tanks, who have at least 3 to accomodate themselves with, making them rather subject to fight design issues than other jobs due to whether the fight is Magical in nature(Titania, Innocence Autos/Tank Buster, Leviathan, Eden Prime) or Physical in nature(Innocence Ult/Spears, Titania Add Phase, Voidwalker, Titan).
This leaves pre-70 DRK in a rather uncomfortable spot. Given Living Dead is learned at Lv 50, there's a way to fix the issue among the Balance Discord:
The most popular way is to make healing become 150% or 200% during Walking Dead, allowing both SCH/AST to have a better time healing and alleviate the issue. The other way is to make Walking Dead only require 50% of the DRK's Maximum HP in healing.