As per Azortharion's guide, Barrage come into the game very very very late, it comes after a long opener of Prepot, Stampede, Multi-Shot, Black Arrow, LnL (X2), now you need to gain enough focus (few Cobra Shots or Focusing Shot) and only now Barrage is used.
For most AOE boss fights, it means that by the time Barrage is used, part of the adds might be already died (or at least the Barrage will over-DPS them).
I'm looking at adds fights that require at least 15 seconds to kill the adds (Beastlord Darmac, Operator Thogar), is the low priority of Barrage is still relevant for such fights?