>>714543573
If you're within effective range, the difference isn't huge, but greatbow's faster rate of fire compensates its lower AR. The range difference is the main thing, and it very often matters at Augur.
Outside of Augur, ballistas and crossbows have more merit since you can use them at level 3-7 and still get level 15 damage with them. Ledges let you cancel ballista's reload animation as well, which makes it significantly better in niche situations.
Rain of Arrows was stupid good in ER, but I haven't had the fortune of rolling it here on a greatbow that got brought to a boss fight yet.