but with the 2 different armor types theres already enemys who are better vs mages with a high magic armor but low normal armor
and the ones who have a high amount of normal armor and low magic armor

making it so ur physical chars focus the ones with the low armor
and ur casters the ones with the low magic armor

so i think it already nice to have a mixed team of magic/physic damage

and since u also get cc´s that go through phys armor check and some through magic armor
u dont need to burn down both armor types to get a cc off

on the enemys that have a high resistance to the element that ur mage uses i would suggest at least using 2 elements (fire/ground for eartch fire and poison dmg for example) its quite unlikely that one enemy has a high resistence to all those elements + u can also take a 4th one in ur weapon
u could also invest 1 point into other skills and swap out ur spells when u encounter certain enemys that have high resistance to ur usual setup
u wont deal that much dmg since u did not max like aerothurge but u still can deal nice dmg with the air spells regardless and its better than going into poison/fire resistant enemys with ur normal poison fire setup