I am in agreement that Dark Knight would be much more suited to come from a new class, that could be tailored to handle both a tank and DD job branching off from it.

Is it possible to make DRK come from pld or mrd? you bet. But being tailored would leave the best experience in everyone's mouths. That goes for any
new job they want to release from existing classes. It will take a lot of work, but sure its doable.