on HW DRK use o have 6956 MP, DA use to cost 1768 efectively having 3 almost 4 uses of DA, without TBN you was able to storage more uses of DA that edges right now, edge it's just more potency that unnecesary increase the punishment of fail TBN.
you forget on SB DA was usable too with bloodspiller, also you forgeth DA was used always with dark passenger you biggest aoe damage attack with 2 and more targets and on HW it was used with dark dance if the pull still was alive to add some handy doges.
the main diference betwen HW and SB is on HW you was able to use DA on 1 GCD per combo as much (souleater) on SB you was able to fit DA on 3 GCD in the worse scenary in a row (syphon, souleater and bloodspiller) aka creating a spaming problem since you wasn't able to efectively use you MP on other things thanks to the dark passenger nerf betwen other things. on HW with the regular uses of dark passenger combined the steady economy with the only option of DA on GCD you have pretty room of precast DA and comfy get the desire effect without need of doubleweaving. DA was a multy-purpose tool with primary uses on DPS allowing combo diversity being versatile and a job that sinergice with his own kit, please don't say the DA spam meme was always a thing of DRK since it was SB exclusive thing.
DA bring diversity depending of you situation, on single target situations use to bring combo diversity, real resource management, diverse uses of you MP combined with dark passenger and the job enjoy a far diversity of GCD, BTW power slash was more common to use on HW so you cann add that to the list in some degree. aoe situations DA was primary used as a self heal since is was better use abyssal drain alone when you don't need inmediate heals, more MP more AD more DPS on both HW na SB, compared to edge and flood that just mimic the same rutine on both single and aoe situations.
edge/flood are just oversimplification locking DRK to spam the same endedless combo without variety, spaming the only MP option you have without variety, no sinergy of any kind, no preplaning/ management, just nothing, storage and use and don't overflow while the rest of the kit is spam on sight, DA give DRK a way to work that no other job have archive a lot of stuff with just a single buttom and adds a lot of variety and diferent strategicts, in other words make DRK a tactical job and not a mindless TA slave.