Interview with xenosys-vex

[Reynhart]

All tanks must be near equal in DPS 1st and foremost. There is no such thing as balancing apples and oranges (DPS and raid mitigation). It works for DPS because 'dps utility' is just raid DPS exchanged for personal DPS. Apples to apples.

They don't need to be equal in personal DPS. And you mention a solution for that, that their utility is translated as what DPS it makes the raid gain.
The easiest utility is having unique damage buffs (Like Slashing Debuff in 3.x), but it can also apply by lowering healing requirements, thus indirectly increasing healer's DPS.
Both of them just need to be on par with what personal DPS the tank lacks.

Just an example : If Sole Survivor would put a vulnerability debuff on the target, it would make DRK more competitive than it is now without touching its personal DPS.