OP was right that Impending Doom was "nerfed" actually. It do proc faster (it say 3 sec faster but it's more like 2sec) but it do less damage each proc. It will summon more imps tough, that's the buff, so on a 2+ targets it summons more imps than the other talent.
- - - Updated - - -
But if you play the game and compare your own logs do you do less damage?