Hello, while this may not be exactly what you are looking for since it could easily apply to any weapon in the game and not just the Longbow, there is another mod called Upgrade Station which allows you to use materials and upgrade items within the game, including the weapons in this mod. Using an Ascendent Longbow with bodkin arrows and no points in melee damage, I hit around 2K per body shot. Which is really overpowered, but since I play singleplayer that doesn't bother me too much. I have encountered no problems whatsoever with either mod and they both appear to run alongside each other seamlessly if that is a concern. Also, I personally would advise that you save the barbed heads and just make tranq barb arrows since they are on the same level as a tranq dart and just use bodkin arrows for damage output as they hit harder and are pretty easy to craft in bundles.

So, I know this is thread necromancy, but if someone else runs into this, it's pretty important to note that barbed arrows are not intended to do more damage on initial hit. If you read the description, they actually do additional damage when the creature who is hit moves around. Many of the weapons in this mod in fact have a "secondary" effect, such as open wounds, which is not a direct ++ damage boost. I don't believe the additional damage shows up in pop-up damage numbers, so you'll need to do some additional testing to see it.