DA is one of the featured mechanics of DRK but while the idea is interesting the actual implementation is boring and spammy. What are some ways to make the class feel more like how a Dark Knight should be?

My suggestion is to increase the mana cost but also increase it's power:

DA Syphon Strike - no longer adds potency but gives a powerful mana-over-time buff that restores mana over 18/21 seconds. This makes it very efficient when used correctly but just a mana-drain when spammed.

DA Souleater - 10% max hp damage to yourself but +280 potency. Basically choosing offense over defense, makes dark knight more "darky".

DA Power Slash - A wild, powerful strike that leaves both you and your target off-balance, increasing the damage you take by 5% but lowering the target's damage output by 5%. Utility.

I'm disappointed with the way DA is now because there is basically no thought or planning to use it atm, which results in DRK being more annoying to play than anything else.