I actually think DRK is the best Tank for ARR.
Souleater is easy to overlook but none of other tanks tools at that level really match it.
For pressure you just spam FOS for AOE and use your Single Target combo to sustain your HP and MP.

Dark Mind is surprisingly useful for ARR content and Living Dead actually works with the Heal check being relatively easy to clear.

HW and Pre-70 Storm blood are where DRK feels like a mess..