At this point PLD will just have to limp along until a full rework is done in 7.0

Sustain vs Mitigation tanks definately seem to be a thing where mitigation tanks will excel in 8 man content and sustain tanks will excel in 4 man content supposedly when realistically and ideally you would want all tanks to be on even footing and viable to the point where no tank has a significant advantage over the others to such a degree where they are barred from content.