DRK ultimate ability living dead needs to be buffed or changed.
Dark Arts needs another level like Blood Arts or change the reliance on it (8 or 9 moves??)
Please do something like Dark Arts + Blackest Nights = ENTIRE PARTY shield since both other tanks have it.

My advice, remove MP and make the blood resource the entire way damage/dps is done on Dark Knight, and put Dark Arts on a GCD or cooldown if its possible.

Just my advice, im no DRK expert. its just an opinion.