Ooof... this is a big task.
I'm not sure if it's the best way to do it, but one way you could
start is to use the spell lists from an older, less-bloated edition of the game. This is only a starting point, though... there is still a lot of work to be done. (Not all of the older-edition spells made it into 5E, some were renamed, others were moved to different levels or classes...) You'd probably end up writing/converting a quarter of the list yourself.
Another way would be to make subclass-specific spell lists. Evokers, Conjurers, Enchanters, and Necromancers all have their own unique spell lists, and there would be only a very small amount of overlap between them--spells like
detect magic, mage armor, and maybe
magic missile would be universal. This would allow for some niche protection between different wizard subclasses, since only certain subclasses would gain access to iconic wizard spells (
fireball and
lightning bolt are iconic Evocation spells, so they would only be on the Evoker's list.
Animate dead and
vampiric touch are found only on the Necromancer list.
Shield and
Counterspell are only on the Abjurer's list. And so on.)
That's a huge amount of work too, and a hefty dose of bookkeeping on top of it. And you'd expect
even more push-back from your players than you're going to get as it is.
That's about all I've got. It's a good idea, but it is a big undertaking. Good luck!