When I reached level 14 with both my Archer and Wizard class, both with the Treasure Hunter talent, I noticed that my Archer had found a lot less spellbooks than my Wizard. My Wizard came across 10-15 while my Archer only found like 5. It appears to be easier to find spellbooks for a Wizard. Or is this a coincidence?
Does your class determine the drop rates? My wizard did however come across a lot of missile ammunition as well as bows, crossbows, fletchery sets etc, so what's up with that?