Any special attack designed to scale with weapon damage uses roughly this formula to represent the weapon damage component:
average damage of the weapon + RAP * .2
More specifically it takes the damage range of your weapon, then adds 20% RAP (which is actually RAP / 14 * 2.8, since 2.8 is the normalized weapon speed used and the weapon damage formula is designed to give you 1 damage a second for every 14 AP).
So yes barrage scales with both the damage of the weapon and your RAP.
With regards to comparison with GT, the primary benefit of barrage on AoE fights is the large spread and lower positioning requirement that allows you to hit a larger amount of targets more reliably. It also provides more burst when the AoE is applied, which is more effective when the spawns are spread out and aren't constant (shamans is a great example since the add spawns line up well with the barrage cooldown- with GT only half of your GTs will actually be hitting extra targets). The longer channeling time can also be useful in cases of misdirecting groups of adds which don't all spawn at once (such as on Immersius).
Last edited by Zeherah; 2014-03-12 at 11:29 PM.
I am corrected thanks for the evidence Illana, and the explanation Zeherah.
^^ This pretty much
The damage out put of GT v Barrage in AoE situations is comparable - but requires a lot more work to pull off with GT (positioning - clumped adds, and picking the furthest target so GT goes through all, and then back through all of them) Barrage - while channeled is designed for AoE and will hit everything in the arc - requires less work to use effectively and so is the easiest and most common choice for AoE fights...