I wanted "subclasses" with actual different powers. So a generalist wizard would be the vanilla option -- she gets all of the possible spells to select from, but she has no special powers. Then, illusionists get some special "illusionist power," like in 5E they can use the 0-level minor illusion more effectively. They have some limitations, but in exchange get special abilities. Maybe necromancers can rebuke undead to command them, using the paladin turning chart, or some such. Different minor-but-generally-useful abilities in exchange for their limitations in spell schools.