I've been pitching that each mental stat should interact with a different aspect of spellcasting since the 3.0 days.

Int - Spells Known/Prepared
Wis - Duration, Concentration
Cha - Spell Save DC, Spell Attack

Also, gate casting behind an Arcana check. (Or a religion/Nature check, as a feature, for Clerics and Druids, or substituting cha for int, as a class feature, for Sorcerer's/Warlocks) That opens spell casting up to whoever wants to roll a d20, including your high int thief who dropped an expertise in Arcana.
Real spellcasters get their baseline stuff for their preparation formula, everyone else is rocking raw int in tricks they've learned in these highly magical societies. Rogues can use their handful of tricks *alot*, but they probably won't be so great at it, ultimately, without the additional focus required to generate a save or have their spells endure, certainly not while lacking complementary class abilities.