The Theft of Essence proc usually just made Dark Regeneration an endurance free power to use (But still needed enough endurance to cast). In a group of 10 enemies, with a 20% chance ToE procs on an average of 2 enemies giving the user about 20 end but DR has a base cost of 30 to cast. It helped but was hardly an endurance solution to DA's end problems. Try out the below to reduce your end woes.
-Start working on the Clubber or Dualist Badge asap,
-Slot for endurance reduction in toggles and attacks,
-Switch to DOs at level 12,
-Slot a Theft of Essence proc into Dark Regeneration as soon as you pick it,
-Slot a Miracle unique at level 17,
-4 slot Stamina and a Performance Shifter proc by level 18,
-Switch to SOs at level 22,
-Get the Atlas Medallion by level 25
-Slot a Numina unique at level 27,
-Take Conserve Power at level 35 and double slot it for recharge,
-Take Physical Perfection at level 41 and slot it with another PF proc.
-Get the Portal Jockey Accolade between levels 45-50.
-Pick Cardiac Alpha and/or Ageless Destiny during Incarnates, level 50+.
I also recommend:
-Switch to IOs when your build starts coming together,
-Don't use Cloak of Fear until you have your endurance under control,
-Toggle off travel powers and unnecessary toggles while fighting,
-AoE attacks use more endurance, only use them if hitting 3+ targets,
-Do not keep Hasten on auto, click it when you need it.