yeah in d&d there are fire + ice gigants too
there is already a spell in dominions 2 : warriors of muspelheim iirc a lvl 8 or 9 enchantment spell which makes your units fire immune iirc .
again i post my idea
perhaps illwinter could include some well balanced player mods as additional themes / nations in 2.13
pvk's amazon empire + thilocks draconian mod so far are good candidates .
your fire gigant jotunheim may be a 3rd one if you make a mod with this yourself