I don't play Mage or Necro (I'm a chanter), but according to the classic spell list:
http://www.crys.org/everquest/spells.htm
The 49 mage fire pet is 200 mana while the 49 necro pet is 490 mana. Isn't that a huge difference when it comes to chain summoning pets? Doesn't seem like anyone has brought this up, so is it insignificant or is it balanced out by other things?
Note that pet casting time is irrelevant because you always dismiss your pet about a second before the new pet spell is finished casting, so i would think this is a significant advantage.