Even if I feel the three tanks are not equivalent, the DRK is the one who has the perfect spell for Tank Buster, it's called TBN.
And since he can put this TBN on him, or on any player in the party, it makes it better than the WAR to protect the team, even if the WAR can make more dmgs.
However, it's really the only thing I see that worth taking a DRK instead of a WAR...
Btw, I've found on Reddit a month ago a table of all tanks enmity's capacity and how many they each give in enmity, and that was the DRK who has the worst enmity, in all points.
If someone has it...