As a non-raider I don't really have a lot of ideas.

Hallowed Ground is kinda OP, but there would be riots if it was changed to much. Its longer CD though seems fine though I'd prefer at 360s instead.

Holmgang, I don't play WAR much and it seems fine enough to me. At most a slightly longer CD for it would be the only thing it would need. Or for WARs to lose a different defensive option to make its increased use more important but I don't like that idea.

Superbolide: Reduce its CD to 300s and its fine.

Living Dead: I know a lot of people want it changed but I honestly love the differences it has in relation to the other tanks. I think the best thing to do is have Walking Dead give a 20% damage reduction as well as causing all actions done by the Dark Knight heal them until they reach full health or die. It'll give a bit of relief on the healers and depending on how much the healing does could even let the Dark Knight do it completely on their own atleast in their burst windows.