FormerlyHemlock
Hero
I actually don't like that either, as the player or GM, that stuff should ideally always be discussed at character creation. I think in a world where no spells are gained automatically this feels much less arbitrary though.
I think this might be the way to go--take away auto-spells from everyone, and then give spells out appropriately. For example, I think you could give all the PHB cleric spells back to clerics and say it's just part of their religious training (they memorize catechisms which act as mnemonics for spells) but not make them automatic for clerics who multiclass into cleric (they don't get the full training, just like they don't get Wisdom save proficiency); the sorcerer spell list is already restricted enough that I think you could let players spontaneously manifest powers (spells) during play when it's dramatically appropriate (in the player's judgment) as long as they come from the sorcerer spell list and then they become permanent parts of that sorcerer's arsenal (no swapping out spells); for wizards, import or re-invent spell research rules which can be used to derive PHB spells over time, in addition to finding them in treasure.
I think a decent spell research system is an absolute requirement to make this sort of game work. That doesn't mean that the majority of the spells in a PC's spellbook necessarily need to be custom-researched spells, but it should mean that if the player finds a spellbook containing e.g. Wish, the player and the PC should both have some kind of appreciation for just how hard it must have been to create this spell in the first place and/or how you would recreate it yourself. That aligns the PC's and the player's respective emotions about the spell.
And then you can do cool things like create a MacGuffin which is actually a piece of magical knowledge, like a 3rd level 12d6 Fireball spell or a 7th level Magic Jar that works on more than just humanoids.