For Living Dead, I don't think changing it is really necessary at all. Unless you're just not hitting your buttons, there is no way that you can run that entire 10 seconds without healing yourself enough. It's like Bloodwhetting on crack.
For Dark Mind, I think they should just bring Dark Dance back in some form. It was an ability that increased Evasion and Parry Rate, but was removed in Stormblood because Evasion as a stat was axed, and we haven't seen it since. It was the physical counterpart to Dark Mind's magical mitigation.

I think the change to plunge was a good one, but DRK probably needs potency increases to compensate for the lost damage. I disagree in general with giving tanks extra unnecessary oGCD weaves because it makes it harder to use mitigation (it's also why I think Salt and Darkness is stupid). GNB is a fucking nightmare in that regard and I don't want a gnashing fang combo or hypervelocity on DRK.

I've seen various takes on how to change TBN but I honestly think they might be able to just remove the MP tax and do nothing else and it might be fine. The frequency with which you could use it potentially makes up for its lack of mitigation otherwise, and it no longer costing MP just means you get an edge/flood of shadow for free as a reward rather than being punished for the shield not breaking.

I think giving Bloodspiller/Quietus a healing effect would be a good idea. I also had another idea to increase sustain on DRK: Give us back a facsimile of what Abyssal Drain used to be. Its current design makes absolutely no sense sharing a CD with Carve and Spit, and I think if you just made it a no-CD spell with an MP cost it'd fill the role of an added MP sink to fill the hole left by removing TBN's MP cost.

Other than that, I think this was a decently well thought-out take.