TBN + Oblation would be better if Oblation was 20% mitigation. It would amount to about 30% mitigation across 3 separate 15 second windows with Rampart, Ob1, Ob2, and then a beefier Shadow Wall window. And I feel at that point DRK at 90 has good mitigation.

Oblation as is, is probably too weak from a Tanking perspective.

A level 82 skill has no business being weaker then Rampart which is 90s CD for 20 seconds as opposed to 10. Rampart does double the work and is available at lvl8.

And the lack of sustain will not help the DRk where sustain is needed or if Walking Dead pops.

Furthermore the best healer to pair DRK with is also the worst since it's going to be pointless using TBN if they will be stunlocked by Holy Spam anyway and then the mob group is dead.

Now raids different story. It very much is White Mage with the chokehold that is Benediction.