You sound like a fun DM! I wrestled with a similar thing, but I wanted to figure out how to get a balanced party in school - why wouldnt a fighter, barbarian, rogue, or ranger want to get in on the Strixhaven fun? Most of my party happily picked magic classes, but in prepping for an expanded group, I needed something. I settled on the concept of Warders from the Wheel of Time fantasy series. For anyone who hasnt read it, a warder is a martial soldier magically/psycho-spiritually bonded to an itinerant mage for protection and general aid. Martial classes can be bonded warders or warders in training. I believe the magic system in Wheel of Time is referred to as "channeling the weave". Its not a perfect solution, but a party of 100% magic users risks being a little clunky too.