The issue with your Living Dead there, is that a lot of the abilities we invuln do obscene amounts of damage, as they're meant to punish a lack of tankswap. If you take two TBs back to back when they apply some kind of Vuln effect, often the second hit does well over 300000 damage (our HP max atm is around 120k), with some having even higher amounts going into the millions (for some reason). This rework would then require that the healers heal that massive amount of HP to save the DRK, effectively locking WHM as the only healer that can deal with the invuln's effect via Benediction.

It works for DK in WoW (Purgatory) because DKs have Death Strike, which heals them for 50% of the damage they took within the past few seconds (and they can back to back two of them if they have full RunicPower), so their selfhealing is obscenely high, it's their whole identity/gameplay. DRK here does not have anywhere near as much selfhealing capability, even WAR in it's current state would not have a good time with something like this, I'd expect.

Though, I do agree that LD is kind of bland with how they 'reworked' it. Just slapping a 'you heal yourself lol' effect on it is kinda lazy, IMO. A while back, before they did the change, I did actually come up with an attempt at a more thematic effect for the invuln, which leaned into the lore and identity of DRK a bit more, and would have more interesting 'downsides' to play around. Unfortunately, I'm unable to find the original post I made about it, so I'll have to rewrite it as best I can from memory:

Living Dead, 300s CD

- Upon execution of Living Dead, grants the status Living Dead, which prevents all damage taken for 10 seconds (similar to Hallowed). Additionally, grants the status Walking Dead for 300 seconds, dealing 1% of the DRK's Max HP as damage per tick (works out as 100% of their HP over the full duration). This damage cannot reduce the DRK below 1 HP.

- Upon execution of Living Dead, the action button for Living Dead becomes 'Borrowed Time', which pauses the Damage Over Time effect of Walking Dead until Borrowed Time is deactivated again, or Walking Dead expires. This gives the DRK a way to temporarily stop the damage from ticking if they need, for example, in preparation for a TB or a 'HP must be 100%' mechanic. However, it comes with risk, as pausing the DOT and leaving it paused for too long means that the damage compiled might be too much to deal with all at once. In a target dummy scenario, it worked out that Souleater alone was enough to out-heal the DOT effect. %-based Mitigation like Shadow Wall would not affect the DOT damage, but TBN and shields would block the DOT for their duration.
Perhaps overhealing could 'remove' duration from the DOT, too? In which case, the 'Bene instantly solves the downside' would still be a thing (as it'd clear the full DOT instantly). Either way, I'm not a massive fan of the 'solution' they gave LD. It's better than the old version, yes, but it could have been so much more