Hallowed Ground has mostly been considered the weakest of all the invulns going as far back as Heavensward, because the cooldown is so incredibly long that you're almost guaranteed to get one fewer use out of it in a given fight than any other invuln. The only thing it was ever really good for was that the actual 'incoming damage reduced to 0' will, occasionally, allow you to use it to bypass a mechanic that's still supposed to debuff you through LD or Holmgang - and Superbolide has eaten its lunch now.
I really think a lot of the discourse around invulns, and particularly around Living Dead, is completely off-base. In a vacuum, the healing requirement on Living Dead is not and never has been a particularly heavy burden. Despite all the histrionics you see whenever people talk about it, in any raid setting, even in a situation where things are kind of going sideways, it's pretty trivial to heal it off. The problem is only relative, when you compare it directly across to the other invulns and find that Holmgang is now strictly superior in every way (and, to a lesser extent, that Superbolide has just a few too many advantages over it for something that is only ever disadvantaged in fights with extremely specific durations that allow an extra use of LD over SB). The healing requirement doesn't need to be removed; it just needs to be respected.
I think if you moved LD down to a 240s cooldown, moved Holmgang up to a 300s cooldown, then squeezed SB and HG together so that Superbolide was at 330s and Hallowed at 360s, you would pretty much solve the balance equation, without having to resort to any more homogenization than we've already had inflicted on us.
