That's because the Gold talents were designed around the original way the artifact worked - originally, there were always "adds" to kill because the artifact itself generated them, the warlock could target and kill them. Except they changed that so now you don;t get those. But they never updated the other artifact talents to reflect this, so basically, they are more orless useless in fights where there aren;t load sof adds.
And guess what, I bet that affliction was "balanced" around the buffs Reap Soul originally reliably gave....but now it doesn't.