Everyone says this sucks and for the most part they're right. Time to see just how much it sucks. I'm not completely sure about the mechanics of volley - as far as I can tell it cannot crit, arrow/bullet damage is not a factor, weapon damage is not a factor, and AP is not a factor. The tooltip says 105 damage every 6 seconds, but Dr. Boom showed me always hitting for 107 or 108 (wtf) so let's go with that.

6*107=642 per target, average fully channeled volley (6 seconds)

Now let's assume we have a lot of time, and can get hunter's mark up on individual targets if we are doing 1:1, but not if we are doing volley. Hunter's Mark starts at 110 and goes up to 440 with each time it's it. Let's say we only have 6 seconds after applying it (roughly 6 seconds, the same time to channel volley), so roughly 6 shots and an average of 137.5 RAP.

Now let's take crit into account. Volley, as far as I can tell, cannot crit. If it can, it must be based off of spell crit or something really small - pretty sure it just doesn't crit. This means that my steadies and autos will have to be normalized for crit, and GFTT and Kill Command will have to be taken into account. I didn't do all the math for those two - but Cheeky did.

Kill Command DPS = 65
Lightning Breath = 183
~= 2 crits
366 Lightning Breath damage
390 Kill Command damage
756 extra damage

Steady:
(150+260.5+.2*2074)+53=878
%30 armor reduction
615 average steady shot non-crit
(863 crit normalized)

Auto:
(93 + 2074/14)*2.8+53 = 728
%30 armor reduction
510 average auto shot non-crit
(687 crit normalized)

6 seconds ~= 3 steady + 3 auto = 4650 damage
Total damage = 4650 + 756 = 5406

5406/642 ~= 9 mobs

So that's why volley sucks. With my gear, I would need to be hitting 9 or more mobs, all inside volley range for the duration of the cast. How often does that happen? Maybe on Solarian... maybe on Tidewalker...