That's a good question which I'm not sure anyone can answer directly. To my knowledge, no real test of pet attack values have been done yet. Only recently has there been the patch making the damage visible and thus somewhat testable. It's still quite hard to control all variables and thus do such a test with any accuracy. However, it's possible to test the relative damage between the pets rather easily. Those tests have shown that the Dire pet does more damage than the Elder (see my
above post for the details). Therefore, if the Elder did indeed have a +3 damage, the Dire would need to have a damage boost greater than 3, instead of only 2.