In the expansion four i would say this is not foolish because some of the new bosses are immune to fire or ice so you kind of have to have a combonation of both to fight some of the bosses others like the ones at the beggining (cronus, gastor, darkon, polgrot, etc) can be killed using only one of them
I was wondering if anybody could post a guide for mages lv 60 through 150 that purchase platabout leveling what items you should get what skills and stats to upgrade etc