I believe the identity of the tanks is mainly present in their DPS rotations, and rather well done actually...

Paladin is the orderly knight, trained to fight to with discipline and in formation, just imagine a two row formation of paladins, front row in fight or flight and the second in resquiescat and then switching.

Dark knight is the agressive one, used to being outnumbered so wont wait to be surrounded and starts the battle by bursting and using everything he has to kill as many opponents as possible before he tires, and then just manages with the basics and magical barries as he catches his breath for another burst.

Warrior is the simple minded tank, thinking is hard so big axe goes in enemy, if i get hit, i heal.

Gunbreaker is the versatile tank, there is always something happening in the rotation and the burst has diferent levels at diferent moments in the fight.