Not testing R1, as its not what I usually play so I have less context to test it against. Plus just doing a first-life Iconic Scourge.
With full stacks of AF, you kinda alternate Sniper and Manyshot on each trash mob, so its about every 3 seconds you get a kill. But yes on Reaper that'd go down a lot. IPS is a lot harder to work with the slow ROF compared to DXB, which I'm used to. Things are weaving in and out between attack cycles pretty easily, and its kind of a carp shoot if you actually line up a multi hit at all, let alone manage to tag multiple mobs with a Sniper or Many. Feels like my old Repeater Arti, though not quite that bad.
I kinda think that IPS will be worthless for Bows, because of that. At least in Heroic, where RP is more impactful. You're doing like 3x as much damage with full AF stacks as each hit on IPS, and there's no way you can consistently hit 3+ mobs at once to make up for that.