Ah weaponmagic is actually Man at Arms - it would be kind of weird not to have that ability on your warriors...
The fights are not supposed to take that long more something like 5 min. Lower the dragons saving throws and just keep it permalock it with status effects.
Which spells do you cast on the Dragon? I look for him and see that he has resistances allmost everywhere. Seems to me, that only sword and bow can make an signifikant damange on him. (Up to 100 Points. not importand as the dragen hast 20000HP)
He has so many spells and AP! He cast Poison and make this burning with fire and all my charactes burn. He (or his companions) cast Water and half the Party got stunt (especily tank and ranger)
Jahan has to Keep Astarte alive and sometime to create an new Ice ELemental. My Firemage cast Speed/Heal on Ranger and Madora and sometimes create a Spider or undeath Knigth(which book)
Ranger and Madora try to hit the Dragon If they not lay stunt or knocked down. The 2 helpers (Ice Elemental und dead Knigth hit the Dragon, if the Dragen Keep them alive one or two rounds)
Maybe class Canon is a solution (especialy for this figth), I try this next time.