So, i created a new character and equipped a bow (I removed the MH before doing so).
I leveled up and added 9 points of dexterity, but didn’t see any damage change. When checking the stat page the bow was missing (i had only the bow equipped). Then i equipped a random sword and the bow appeared. Upon removing the MH sword the bow stayed in the stat page.
Basically, just equipping the bow with no MH leads to the bow not gaining any stats. You have to equip a MH.