and....
Christ Crispies...
You have, at max in the most ideal of situations, a 20 second window where you cannot die to most mechanics in the game once you press Living Dead and activate the skill. The only place to go is not die (wasting the WD phase) or take fatal damage and pop WD and not take further fatal damage for 10 seconds. You no longer need to mitigate for yourself at that point, nor do healers need to be concerned with your HP for a temporary period of time. This means they can spend their time doing other things, like getting in a few GCD damage spells or handling other mechanics.
The question is does it play out that way where you get a max effect out of it? Usually no. Normally you would use it before a fatal tank buster cause it's easiest used that way, but you could pop it earlier than the buster and not worry about other damage so long as you dont take fatal damage before you need to. As for cleansing WD, yeah you can do it whenever, but if you got a WHM with Bene, theyre a bad WHM if they pop that bene the instant WD procs. There is no need to do it then. Normally most WHM will wait till around 2 seconds remaining on WD to pop bene. Other healers might have to start healing you sooner cause of the nature of the skill, but thats a separate issue.
Im not defending the skill cause I think its fine, but rather this concept that "Oh, its only a few seconds" or "its not really that long a skill" or what not isnt accurate. The reason why the skill has that heavy burden of being healed for a value equal to your HP is solely because of the potential effect the skill has. The fact you can essentially stop receiving heals for 20 seconds at most would be a pretty big boon in most fights. Conceptually it is incredibly strong, but how it actually plays out is another story. People dont abuse the LD phase because of how jank it is to begin with. A random SCH shield or reprisal from your cotank can mitigate enough damage where you dont take the fatal hit like you plan, LD falls off, and you get critted at low hp and die. The fact its harder for SCH and AST to heal you up, while WHM is just push Bene and win makes it unusual, or the fact that you can actually wipe out the invuln effect early through healing (of all things) makes it a liability as a invuln. Pair this with the fact that DRK has some of the best mitigation as a tank thanks to TBN, its really not an ideal Invuln. It doesnt synergize with it's own kit.
Frankly with how the DRK kit is currently, it would actually make more sense (kit wise) for DRK to have Holmgang, and WAR to have LD simply cause DRK can TBN themselves at the end of Holm gang as to not take fatal damage at 1 hp, and War actually has the ability to self heal up to 100% hp when LD pops. Even thematically it feels like it might make more sense - Lashing yourself to another target, refusing to go down in a brutal act of attrition for DRK, and refusing to fall and coming back from the brink of Death as a Warrior through bloodlust.
Point is skill is jank. It offers up the longest 'invuln' period of all the invulns, but only on a technicality. It is easily the worst invuln of all 4.