In your darkest hour: DRK's identity crisis

[Reynhart]

Cecil is a beast.

As a PLD, yes. As a DRK, he has the worst stat growth of basically every character in FF IV. And frankly, when comparing to a BLM and a WHM, there's not much competition on sturdyness.
And having high pysical damage is exactly what would make you end as a DPS in an MMO...even if PLD-Cecil also did more damage than everybody else...

Other dark incarnation

The staple of the job is still losing HP to deal great damage. This is not what you want for a tank...and precisely why they made FFXIV iteration spend MP instead of HP.