Why did PLD get such a buff

[Syzygian]

You raise a fair point. Since Dark Arts is the DRK's main gimmick I feel Dark Arts should have an effect on the HW gained skills. Only AD and CnS have this. Salted Earth, Plunge, and Sole Survivor having enhanced effects would be interesting to see.

You have to be careful with this. DRK's rotation is already a veritable sea of button mashing without giving everything DA effects. Giving things like Plunge and SaE DA effects, you'd have to not make them *too* good or, between those and DP/DACS, DASE would barely have any room in the rotation.

Any added DA effects would have to be on situational abilities and not things that are a regular part of the rotation, which is already incredibly busy.

[Reynhart]

You have to be careful with this.

Easy.
Increase Soul Eater's basic potency to 350, and make Dark Arts only increase the leech effect to 150%. There, one less skill where you would use Dark Arts as an OT. It would probably be a little DPS loss, since you use DA on the majority of Soul Eater, but it wouldn't really be a big deal.
It's the same for Dark Dance and Dark Mind, wich are not very useful when you're not MT.

This way, you could have DA+Blood Weapon refill HP or TP, since you'd need less MP back.

This way, wether you're MT or OT, you wouldn't spend Dark Arts on the same thing, and you could have a very different feel and a distinct utility.