When would you take DRK over PLD or WAR?

[Adrasteia]

Is this a confirmed thing? Can't help but be somewhat skeptical.

Most of Warrior's "big DPS" numbers come from Fell Cleave, which is dangerous to try and use while MTing (except in specific circumstances, like during Liberation), whereas Dark Knight has no such restrictions and can parse similarly high to Warriors without Grit (910 is the highest I've seen, versus about 1000 for Warrior). The issue is mostly sustainability: Warriors can keep going indefinitely, while Dark Knights and Paladins will both run out of TP at about 2:20 of continuous ability use.