Assuming we're keeping 5e structures in place, you give the caster classes a small, bespoke spell list (4-5 spells per level or so) at the end of the class description. You format it to look like cleric domain spells (i.e. spells are listed horizontally by level, not vertically). You also give them the option to swap out a spell on their spell list each level for a different spell from the book, normally with restrictions. A summoner might be able to swap out for any conjuration spell, for example. A more versatile caster might have a feature akin to bardic Magical Secrets, or have a spellbook that can gain spells from the wizard list.
In a hypothetical revised or new edition, I have spells and maneuvers in the back of the book, organized by spell/maneuver school plus some other thematic organizing principles. Like Arcane, Divine, Primal or White, Black, Blue, Red, Green or Damage/Buff/Utility. Something where you can slice and dice by multiple categories to restrict access to an organized subset, and then do the same as I mentioned above.
I guess my problem with this is that it highlights the very issue involved:
Spellcasters now, at least conceivably, tap into dozens of pages of at least
possible options, even if each individual one only taps (say) a dozen pages in total. But it also gets two pages' worth of class features. Non-casters...just get two pages' worth of class features.
That is, and continues to be, the fundamental issue. Casters simply get to play
more of the game than anyone else. It's not like Shadowrun, where mundanes have cyber-augmentations and hacking/drone work, which are almost totally off-limits to casters (as cutting up your body directly reduces your Magic stat). There, at least the mundanes get their
own, distinct rules-subsets to play with, some of which can be incredibly important.
Branching off a bit from what you specifically said, TwoSix...
Doesn't anyone else at least think it
fishy, even if you don't agree that there's a problem, that it's
consistently one side getting shortchanged and not the other? Like, with the sole exception of 4e (the edition that got criticized for being "too balanced"), it has essentially
never been the case that Fighters do consistently better than Wizards. At early levels, you may have some times where Wizards just don't have enough oomph yet. But even in games pretty much purely ported from early-D&D (which I
have played! A little, but still!) I have seen a Wizard of something like 5th or 6th level--high enough to cast
invisibility--absolutely blow every other player's contributions out of the water because of what a single spell could do.
And that's not even touching on how magic has
always allowed for the creation of entirely new spells. Where do people think
Rary's telepathic bond,
Snilloc's snowball swarm, and
Tasha's hideous laughter came from? These were players
inventing new mechanics for their characters. Since when have Fighters, and their "mundane" brethren, been able to
invent new mechanics for themselves to use?
We're not just talking about characters that get to play
more of D&D than other characters. We're talking about characters that get to
add more to the game than others. There are vastly more remembered spellcasters than remembered non-spellcasters; the only Fighter of old whose name I can remember is Robilar, and even looking over the list of Fighters on the Greyhawk wiki is...not particularly inspiring. Fighters tended to be henchmen, retainers, or minor figures. Wizards
shaped empires and
ended wars.
