Honestly, I'm pretty okay with classic vancian casting. At least in a general sense. It just needs improvements. Like not sucking for one. The concept is cool, but actually being a wizard isn't like what people upsell. They are either lying, omitting important things, or playing at a table that ignores half the rules that govern magic.

That said, the idea is sound. You just read the spell. So long as you understand what you are reading, the spell is shoved into your brain. Ready to simply unleash in an instant later. The more you do this (which is the same as studying magic), the more you can shove in your brain at one time. I'd alter the specifics so you the wizard isn't the most trivial to cuck class in actual practice, but the idea is great. Can overlay easily on some other, more esoteric, system. For instance, what's actually going on is far more accessible than wizards teach, but the cover exists for a reason. It focuses the phenomenon into a generally more potent and safe methodology. You won't kill yourself with it in the same way a power lifter can accidentally kill themselves lifting too much stuff. If your 'slots' are spent, that's that. A 'miscast' won't accidentally overwrite your existence to having always been a particular kind of desert dwelling rat either. You just lose the spell for the day. Isn't that nice? You just gain some, entirely manageable, limitations for these protections.

It explains the elitism around it well too. It's pure gatekeeping. Very warranted gate keeping. Granted, you could always do without it. You gain quicker, flexible, on demand power. Just try not to find out why Goku is responsible for sucking up more pure miracle cures than any other person in fiction ever.