Honestly, I never gave it any thought really. I do see how feathers would not present as much of a barrier as vanes (especially blazers or fusions) because they would lay down. Stiff vanes will have to "force" through, so to speak.

However, I think (for hunting) in most cases is IS a trivial point, because the hole the vanes or feathers is following through a deer, is not one made by a field point - its much bigger. That is why I don't subscribe to the "thinner shafts penetrate so much better" theory. Sure in a target that is gripping the shaft they do, there is less shaft to grip and slowdown. But following a broadhead swath through an animal, I don't feel it really matters.