I'd say it's an oversight. I tribble tested it with stormshade when they first came out. We (the people) voiced that the carriers were fine but got a little out of hand with 3+ spawning fighters and whatnot.
this is an easy fix... pop them before they get all the spam out! muahahaha no but I agree targeting is the issue.... I think that you should have 2 different targeting mechanics... click to attack npc's then click on chracters to attack and only see real players. easy as that... that way you dont have a map full of red, which will help graphics issues and get rid of the free to spike problem.
Would be a great solution.. I dont think its the pets themselves tht cause lag, but rather the targetting boxes - trying to pick out a target among 50-100 targetting boxes can be a pain tbh, even without the lag.