I think it makes sense to classify all of the pets as <Pets>. It would be inconsistent if some pets were <Minions> and others were <Pets>. That having been said, I think Pets doing ~55% less damage than Minions is too harsh. It would make a lot more sense if pets did the same damage as minions but had a lower damage cap.
The bottom line is that I think that this fix hits Phantom Army too hard. I can't comment on Fire Imps because I've never used them. It would be good to see one of the following changes made to Phantom Army,
-Increase duration
-Reduce recharge time
-Increase damage
-Reduce endurance cost
Some combination of the above would bring Phantom Army back into balance. Too much was taken away and not enough given back.