All three are capable of doing content effectively, even if one is grossly disadvantaged by simply having it's fault ignored repeatedly, they all three can perform their base function, that being to tank. Warrior and Paladin simply excel at it compared to Dark Knight. Warrior is seemingly based around the idea of doing more with less, Paladin has a cooldown and utility for almost every situation, and Dark Knight is the opposite of both and requires vastly more effort to achieve the the same results with no consideration or extra reward for the effort put in to doing so.

Quote Originally Posted by HyperiusUltima View Post
but with all the anti-climactic ‘doom and gloom’ over Dark Knight.
Honestly, for Dark Knight, it's not doom and gloom when it's the absolute truth.
Poor mitigation, lacking in offensive ability and an over reliance on multiple, separate resources.