How is this change punishing the user for other players misplays? Giving The Blackest Night an extra effect to remove Walking Dead while giving the shield ability lets the user correct other player's mistakes by letting them survive with their own invulnerability skill properly without relying on others.
Skills that do [x] instead of [y] under buff [A] or buff [B] exists already - AST's collective unconscious is a prime example. We also have Monk's Dragon Kick and Bootshine being the best example here. Under the status effect of [Leaden Fist], Bootshine's effect gets a potency change. When under the effects of [Walking Dead], The Blackest Night's skill activation can simply be coded to remove Walking Dead's effect if it is active. The barrier is a separate buff from the skill itself.
This would be a Quality of Life change as you should still be dependent on healers to adjust and remove the walking dead buff since walking dead only stops your HP from dropping under 1 in group content.
However, in the event the healer dies or you're playing solo content, you can use your invuln with The Blackest Night without strictly requiring a healer to save you from the Living Dead's killing effect. The Blackest Night may remove Walking Dead from killing you and giving you an HP buffer with the shield, but it won't restore your HP - as is with all invulnerabilities.
The only problem here would then be if you somehow popped The Blackest Night 5 seconds before you turn on Living Dead (which makes no sense why you would shield before activating the invuln since the invuln loses its effectiveness) and then wouldn't have The Blackest Night available to remove your Walking Dead status.
I'd agree with you here. The effect can be a trait tied to living dead that changes walking dead automatically at lv 70. Then again, you also have people who complain tanks play all the same and are carbon copies of each other. The invulnerabilities are at least somewhat unique with each job having their own caveats with their invulnerability so I proposed an idea to keep the skill's uniqueness rather than make them similar to the other but eh. I guess people also like the idea of going down the route of turning Living Dead into a better Holmgang/Superbolide with different animation effect.