DRK is straight up my least favorite tank to heal in Savage. They're "fine" but I find myself mentally wishing they'd reroll and play any of the other tanks, which isn't a good sign. In many cases immunes are the easiest way to handle a tankbuster because it saves resources, but DRK demands them. Even if I'm a WHM, you're locking me out having freedom on of one of my strongest single target oGCD's.

Holm and Superbolide aren't too much penalty because you don't have to heal the tank to full. If they're swapping, you just need them above the threshold of the next raidwide, which deal less to tanks anyway, then raid heals take care of the rest. I don't even panic at random Bolide's in dungeons because, hey, I have 8 (soon 10) sec of comfort time. Bolide is especially comfy because they aren't taking damage for the full duration. Holm is the best raid immune in the game due to the recast time, allowing multiple tankbuster uses that other tanks won't get.
It's a good point too that you rarely get the full 10 sec from LD. As soon as you're healed, it's gone. Other tanks will always get 10 sec now.

TBN is just overrated at this stage. It seems to be the sole crutch for DRK, "oh we might be bad in 10 different ways but we have the best mitigation cd!". It's obviously strong, but abilities like Nascent flash are amazing too, far easier to use and to ensure they're dps neutral. This is only made worse in Endwalker where the other tanks will get even fancier toys and stronger self-heal while DRK is putting so much weight on that single crutch it's going to snap.