- Attack: Dark Knights can get absolutely absurd amounts of attack (I have seen over 3000 ATT with soul eater up!). They have much higher STR and attack than BLU, so they can easily cap attack without support. So Fury isn't as important for them. However, accuracy is harder to reach, so you could probably drop Fury for an Indi-Torpor or Precision instead.
- Haste: As far as Delay Reduction, the DRK wouldn't need the GEO to haste them. With Apocalypse, a DRK can cap JA haste without Hasso, which is notable because that means they can reach 80% delay reduction with just a Haste II. With Caladbolg or Liberator, they can still reach 75%. So assuming the BLU diffusioned Might Guard (don't be selfish, BLUs), then the DRK can reach 75-80% with just a Haste I from the WHM, thereby eliminating the need for Indi-haste entirely. (It's worth noting that a Dancer can also cap with just Haste I, or by picking up an extra 10% DW in gear)
- Absorb Spells: A Liberator DRK with Nether void can absorb up to +69 of any stat. That gives a lot of flexibility as it's a very potent buff AND debuff. That fixes the accuracy problem, since they can nethervoid Abs-AGI for -34 eva down, and then Absorb-ACC for about 54 acc.
So in the Party example you gave (DRK, BLU, COR, GEO, GEO, WHM), I think the DRK would surprise you. Also don't forget the corsair with Chaos Roll. You get an
extra 9.7% attack bonus just for having the DRK in the party. However, I wonder if you'd get more damage out if dropping the offense GEO in favor of a RDM instead. A Liberator DRK and a RDM with capped enfeeble should provide close, if not more, EVA-down as an idris geo and would cap haste on the DRK. Also, between the DRK, BLU, and COR, you have 3 weapon types. So 3-steps with inundation should be a sizeable damage increase.