I will start off just by saying - I really like the idea of having a PLD and DRK pair in a group, being a defensive minded player. I know that is a big dps strain, so you will never see that in higher-end raid content. Me being me, I really would like to see DRK being a relevant OT with a PLD but still be able to pull numbers similar to WAR, and still be ok as far as dps is concerned. Please keep in mind, I have done no number crunching, this is less than a day of thought and this is straight from brain to page

I think a cool idea for an ability for DRK is something that would strictly be used as an OT. Its ability would be:

Increases damage granted by Darkside from 10% to 20%. Can only be used when Darkside is active. Cannot be used while Grit is active. Changes Dark Arts effect of spending mp to spending hp (this helps bring back the lore of a DRK using its life force to increase power) Shares a recast timer with Blood Weapon.