I'm not sure why they increased arn auto attack damage to that extent rather than just have pets scale more in line to what they want, but thats just how it is.
its a bit funny because Yoshida said at one point that books weren't going to be any more than scratch damage (like wands/staves currently are), but they ended up being substantailly better than the others.

At any rate, thanks for providing some insight. There's a fair few people saying stuff when they don't really know anything, so that provides a bit of clarity.