(Psi)SeveredHead
Adventurer
It wouldn't be to everyone's tastes, but you've got me thinking about a D&D edition (or just variant) in which the spellcasting classes' powers/abilities were innately superior to those of the martial classes--but in which the "assumed level" of magic items was explicitly higher for the martial classes, and in which there were far more magic items that could benefit a non-caster than a caster.
That was called 3.x. Really. Wizards were more powerful, but a fighter's items were more useful. Overall... wizards were still more powerful.
That might work for some people, but I'm not a fan of items. My current campaign is set in Dark Sun. It's inherent bonus-using. The rogue PC has a throwing dart that copies a 3rd-level magic item (one that does ongoing 5 fire damage once per day, anyone know what that's called?) but it's a non-magic poison dart that does ongoing poison damage instead. Oddly, I was actually praised for having that a daily item rather than a make a Nature check item, perhaps due to the lower bookkeeping.
In D&D terms you might say that a demon or other supernatural creature has damge reduction (or even invulnerability) against normal attakcs, but vulnerability to magical ones. Hit it with an ordiary sword and it has little to no effect. Hit is with a magical sword or a spell of rebuke and it suffers - moreso than a mortal human being would.
It was almost the opposite in gameplay. A wizard beats a warrior easily; cast Hold Monster, or Greater Invisibility followed by Lightning Bolt, etc, whereas a demon can probably resist half the wizard's spells. (A warrior might have the right weapon, or can just power through DR; given how weak monster ACs often were, Power Attack was a very powerful feat.)