I can tell you I USE all 4 of my pets a lot. At least 3 of them sometimes in a 2 or 3 hour solo, and probably 2 of them in a group setting. They all have a use in certain instances. If you only use the Fire pet you are really not taking advantage of half your ability to engage, split, CC etc.
A Mage is a lot harder to play well than most people think. It is not all send in the fire pet and sit on your ass like a LOT of people do on here if you really want to make a Mage really stand out. But I am not knocking people that do it, but they are missing the fun of the cat and mouse stuff you can do on a Mage. They are damn powerful played to the max. And if you are lucky enough to ever have the Epic, and The Burnt Wood Staff ,
http://wiki.project1999.com/Burnt_Wood_Staff, Wow hold on. Killing machine.