Looking at your numbers I would guess that speed (or dps) doesn't necessarily affect the skill damage as much as the base damage of the equipped weapon, both high and low damage, does. Otherwise, there would be a much bigger increase when Sunblessed Bow is equipped in comparison to SentGun, but instead they're almost identical.

That's the one thing that sticks out right away.

I'll try to help look at the numbers a little bit more.

Thanks for your table