Since when does defence skill help in all directions? I thought it was clear that it only helps from the front and the right side.
I never run a test, but I don't believe that experience doesn't add to range attack. I had silver and gold chevroned slingers and they annilated everything and I never heard anything different.
The reason the test you recommend doesn't prove that is because EB phalanxes are invulnerable to any range attack from the front, so you are right more attack doesn't help there.