I tend to prefer hard magic in my own designs - But much like technical studies in real life, no one is a master at it, and even the very best mages still discover new things that surprise them.

This way you can have very knowledgeable mages who know many technical specifics but miss the forest for the trees, while a total amateur mage might accidentally tap into doing something that's never been done before.

I really like how Eragon does it: magic is a manifestation of the wielder's willpower and strength. If you overexert, you can pass out or die. However, gemstones are capable of storing mana for later use, and your capability with magic can be improved with training.

I feel like it's be possible to accomplish both by creating a system unbelievably complex, something akin to Tolkien creating the languages for his world. You could understand it, but it'd take maybe three weeks.

To me the ideal magic system has some direct way of interacting with the narrative and themes; it's something that is somehow meaningful (at least to the characters in the setting) beyond just its instrumental uses.

Hard magic seems like an unavoidable perspective. Once someone casts spells daily, those spells become familiar.

Tolkien avoided this problem with limited spells. Le Guine leaned into it so hard that the method became enchanting. The reader could see Sparrowhawk's point of view and start to wonder more about the rules of magic as they trickle out slowly.