I played a DM/SR scrapper and a Dark/Dark Defender to 50 way back when... The Dominator Dark Assault choices are a mix of those 2 attack groups.
I have played with all of them, but have settled on Smite, Gloom, Nightfall, Life Drain, Gather Shadows and Midnight Grasp as must have powers.
I don't slot Dark Blast or have it in my tray, but do use Sands of Mu and Blackwand to fill out my attack chain. So far I am lv 23, and have not used the higher stuff with this character, but have on previous ones years ago.