Darks already have very good mitigation.

Basically at the start, Darks (mostly X -DPS) could not understand how to tank, and got a bad rap over it.

You have 2 normal damage reducers (like other tanks) and 1 that has a TINY cooldown (1 minute!) and you can throw it ontop of the other two in any magic damage content to pad your health. Dark Dance is less powerful than bulwark but lasts 5 more seconds and has one third the cd.

Basically Dark Knight is not about having tons of cooldowns like a paladin, but having good ones that are up very often.