I don't know if you know this or not, but different types of arrows have different damage modifiers. Iron and steel arrows are amongst the weakest arrows. But I can say that bears are the biggest damage sponges in the game.
Yeah, I know about the first part.
Right now I'm using glass arrows AND equipment enchanted with around +60% bow damage total on top of the perks.
Bears seem to just not want to die.
Mudcrabs, too, sometimes soak up an inhumane amount of damage. I remember one time a dragon spent like 5~7 minutes chasing after a single mudcrab. By the time I finished killing the dragon the mudcrab was still alive. And yes I'm positive it was the same mudcrab