We've been struggling with this problem on red for years - Ambrogio asked us to compile some information. I thought I would post it here since this is the same bug.
Here is a video demonstrating that archery bonus damage comes from the delay of the main hand weapon.
https://www.youtube.com/watch?v=SJ1iw6lOJ-8
The warrior testing here has a Weighted Axe and Bow of The Huntsman equipped.
This is obviously not how archery should be calculated - there is a flat 100 unmitigated bonus damage on each hit.
Using a fast bow and vendor junk mainhand produces vastly more DPS than end game "Best in Slot" equipment.