Huntsman skills scale off Basic Attack damage. Simply put, it scales off not only the weapon base damage, but also it's required ability (Str, Fin or Int). It works just the same as warfare and a few polymorph skills. However, you can't use Huntsman skills with anything other than Bows and Crossbows, so it's not a versatility, I believe it only works like this so it can scale off your weapon damage instead of having fixed base damages.
