Bring Back Scourge!!!

[EusisLandale]

They could totally buff other potencies to make up for the loss

They did.
30 seconds: 1 Bloodspiller = 380/475, 3 Souleater combos = 2040, HS, SyS = 400
Total: 2820/2915
Now count in the 5% increase compared to now on Darkside: 141/145
Finally pair that Darkside gain up with Bloodspiller, used just once every 30 seconds in Scourge's place.
141 + 380 = 520
145 + 475 = 620
This is already a gain over Scourge without using any additional GCDs. But here's the thing, Bloodspiller can be used more than once every 30 seconds without losing any of its potency due to overwriting and its own potency is higher than any GCD it ends up delaying.
Then you count in Darkside buffing auto attacks, Carve & Spit, Plunge, Dark Passenger, Salted Earth, and every Dark Arts boost you can squeeze in.

We didn't lose Scourge, we got the bulk of it able to be unloaded all at once and the rest of it baked into everything else we do. I wouldn't be too surprised if Bloodspiller and Darkside's buff compensates the loss of Reprisal and Low Blow too.

As for the cost of it, given that The Blackest Night will be the source of the vast majority of our Bloodspillers, every second one can be seen as where Darkside's MP drain has been moved to. The other? It shares a cost with Dark Arts and will push out a part of our combo; A 230/325 Potency Gain over Hard Slash, 130/225 over Syphon Strike, and 100/195 over Souleater. This is, in four out of six possible scenarios a higher MP to Potency conversion than Dark Arts can manage and is applicable to taking up two slots DA never can.
Simply put the loss of Scourge compared to everything we gained is not a loss at all in potency and very rarely even able to be considered a loss in cost efficiency.