Living dead still only provides 9 seconds(AT BEST FFS) of actual mitigation while having a 60 second longer cooldown than Holmang, the best invulnerability skill in the gane.
All the downsides of Living Dead are for an extra 9 seconds to time the invulnerability for a death blow in high end content.
That sounds fair enough on paper, but it's not nearly practical enough to compensate for it's downsides even in highly coordinated groups.
Few deathly tankbusters in the game possess such stringent timing to facilitate the use of a buffer window.
Titania EX is the only I can think of off the top of my head that truly benefits from one.
If anything, I'd argue Living Dead encourages bad habits.
By getting used to the safety net provided by the Living Dead Window, you may neglect to actually time the invulnerability accurately - instead, shifting the bulk of the burden of timing mechanics to your healer while having them have to waste an unparalleled amount of healing resources than they would have to exhaust on any other tank.
With Endwalker, Warrior and Gunbreaker will have an significantly easier time timing their invulnerability skills properly for high end content, while DRK's pathetic excuse for a cooldown still has to worry about ending their mitigation window early.
Speaking of dungeons, pulling wall to wall will offer ample opportunities for tanks to utilize their invulnerability skills if the tank and healer cooperate to conserve their other resources during the activation of the skill.
Some tanks exercise the use of a macro to callout the activation period for invulns in advance for PUGs, which even Paladins should use so a healer doesn't waste a regen or shield on during their absolute invincible period.
Living dead is so utterly demanding of healing resources that you're better off not risking using to squeeze out an extra bit of optimization during runs, let alone as a panic button.
DRK is also the only tank that can't benefit from their invulnerability skill during solo play...I could go on...but many people have made it quite clear FOR YEARS just how aggravating Living Dead is.
It's bottom of the barrel gameplay design that cements it as not only my hated skill in FF14, but possibly any GAAS I've ever played.
The only positives I could sing Living Dead is that it looks cool.
Which is practically the thesis of DRK's entire design post HW and TBN.