One change to dark that would literally make it 100% better.

Change the effect of Dark Arts -> Dark Mind to: Apply 15% magic resistance to all party members in range. GG. Thoughts?

While that could come in handy, PLD and WAR would still be able to it better, for free, and cover both types of damage. Doing fights at lower level would also make dark even weaker than it is already, since you don't have TBN there. In terms of party defense, I would rather have them give DRK a debuff based party mitigation skill that fits in with the retaliation part of the job (ahem previous Reprisal).

Homogenization isn't the solvent to the problem, so no -15% Magic Damage taken for the party at the cost of 2400MP and a 60s cooldown is actually not fixing the issues of Dark Knight.