DRK - Excessive Dark Arts

[Crater]

To this day, I still dont understand why it was a potency loss in 4.0.

Because every three Bloodspillers that you use means one fewer Souleater combo, one fewer Syphon Strike worth of MP, and one fewer Souleater worth of Blood.

One Syphon Strike gives you half a Dark Arts worth of MP; Dark Arts is worth 140 potency, so that's a loss of 70 potency, down the line. One Souleater gives you 10 Blood, which translates to extra Bloodspillers down the line.

Taking the opportunity costs into account, it was a slight loss. Now it's either a slight gain, or at worst DPS-neutral, assuming you break every shield and never go over your Blood cap.

[Shinkyo]

snip

Thank you for the clarification!
personally, I'd still use TBN as much as possible (for every damage spike) even with a small DPS loss because it just feels so good to plan the shield and use BS as a reward :-)