A pet's ability and auto attack are based on both weapon damage and intelligence of caster. I just did a bit of testing on this, and its easy as day to see this is how it is. Swapping out weapon damage with something much lower will drop pet damage. Taking a substantial loss on intelligence by removing equipment will also lower pet damage as well. Parser and the eye test indicates both of this. Not how much it scales up isn't something I have a lot of analysis for, but it would be safe to assume these two factors are probably the primary reasons why. As far as why a pet and a summoner shares similar auto attack damage; I suspect your character is used as a basis with each summoned pet mimicing the stats you have while differently scaled in terms of vit or int. 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.