Alright I believe I've reached a result with the Blood Gauge version after some heavy thinking. Here's the link, I will also update the OP with this after posting.

https://docs.google.com/document/d/1...it?usp=sharing

The notable changes:
  • Edge and Flood of Shadow are both introduced at lvl 74 and are our Blood Gauge spenders. I did not include Edge and Flood of Shadow here. They both cost 50 Gauge.
  • Scourge is now a GCD DoT we maintain, near identitical to the HW version except it has a higher base potency and longer duration.
  • The Dark Arts combo bonus from Power Slash, Stalwart Soul and Bloodspiller (formerly the placement of Scourge), now increases the Blood Gauge by 25, to keep it in line with 2 combos equaling 1 use of my Dark Descent version.
  • Bloodspiller now is the upgrade for Souleater and Quietus is now the upgrade for Unleash. Both while Darkside is active, of course.
  • Dark Mind has been reverted back to it's original form. You get it at lvl 48 now, since Shadowskin remains as a lvl 45 unlock.
  • Blood Price is removed and Sole Survivor is now back. Sole Survivor functions near identical to how it did in latter Stormblood. The only difference is it solely is HP recovery, and not HP and MP recovery.
  • Salt and Darkness will now spread Scourge to all enemies inside Salted Earth

The reason I didn't include Edge and Flood of Darkness is because there simply isn't room for them at a low level, and I don't want to introduce the Blood Gauge too early because that would mean pushing other abilities back, making the leveling experience worse.