I think can answer that one. I didn't like StB DA spam compared to edge spam because of the doubled (relative) consumption of DA in StB when compared with its consumption in HW. Edge doesn't compete for any of the rest of DRK'S toolkit other than TBN, and it's much easier to hang onto 3kmp for that than working with DA was on the whole in StB.
Often in StB DRK you could get locked out of applying DA to an oGCD because they not only reworked the only GCD combo finisher that did not consume DA (Delirium), but applied the same flat DA bonus to a second hit in the combo (Syphon Strike), which you also HAD to press to generate MP given the constant drain from Darkside if you were between Blood Prices and Weapons.
Because of this, it actually exacerbated the floor of using MP for mitigation when they threw in TBN and more double weaving required so you didn't eat your DA on a flat 140 potency buff to your next GCD if it wasn't Hard Slash. Not to mention, TBN, DA and Dark Passenger all costed the same, so that was like 60% of your MP bar if you used two in conjunction, and saving that amount meant overcapping was not so hard to do when you were in Blood Price/Weapon.
DA went from "enhances your strong actions" to "applies 140 potency to probably your next action" and became more like a chore at best or a hindrance to using my enhanced dark mind or passenger at worst. It had the same treatment as AST cards got going into ShB, and the fewer amount of free time to use it (no scourge, no pre-syphon strike oGCD, more time spent in blood weapon with new Delirium) and less MP to work with (no Blood Price out of Grit, higher cost on all spells and TBN competing for MP now) just made it feel more like filler than a feature.
Not to say I don't miss DA. I just think it worked a lot better in HW when its cost was lower and it wasn't consumed by 2/3 of your basic GCDs. Maybe if they untethered DA consumption from one of the only actions always available to build MP, and used, I dunno, THE MP BAR for DRK's gauge in StB instead of Blood it woulda been received better. That's basically how it works today, except it has WAR fell cleaves slapped on there cuz everyone loves Fell Cleave. Bloodspiller could just have been a high MP cost big attack, maybe costing "up to" like Flare, or like Eventide does in PvP.