So it turns out you were right to question, but not for the reason you did...
Vakeva can't change the bane on his bow. I had just finished rolling a round for a high level Inquisitor in another game who can, and just kept right on going with it.
Vakeva's bow is just evil outsider bane. Scotley, please don't count the bane damage vs the gargoyles, and change his enemy selection - he'll shoot one 'till it's dead, rinse and repeat.