DRK needs more self-sustain in dungeons

[Silver-Strider]

Then you'd need to create other design elements to make them more distinct defensively, as they would just be near carbon copies without the variation of sustains used to define them more.

That was somewhat how it used to be.

WAR didn't have damage mitigation like PLD and DRK did, instead increasing their Max HP and increasing the amount of healing they received.
DRK had a constant MP drain skill that would empower their damage but managing their MP was a big part of their gameplay since some of their tools required MP to use, such as Abyssal Drain being a GCD that used MP to deal damage and restore HP.
PLD was just the mitigation based tank.

It wasn't balanced all that well but it was doable.