This is why I say more classes.Oh, I don't believe its possible for a high level martial to exist without supernatural abilities in a form I'd want in my game. It would require you either radically redefine what "mundane" means, or that you go narrative, neither of which are acceptable options to me. At some point you have to flip that switch.
If other people want to advocate for that, that's fine.
Because there are some fans that say mundane martials have an upper limit before high levels and that non-caster would be required to have magic items
And there are some fans that say mundane martials don't have an upper limit before high levels and that non-caster would be required to have supernatural nonspell features.
A Fighter with a +3 Armor, +3 longsword, and a shield of fireballs.
A Barbarian with 30 Strength and 30 Constitution who can lift as if Large size.
A Monk who can run up walls, stand on water, teleport, and shoot ki blasts.
A Knight with+2 longsword of kings, and Expertise in Persuasion, History,and Athletics.
A Warblade who can attack the strands of reality to create air blasts and planar gates.
A Marksmen who can craft and shoot arrows with masterwork, alchemical, and/or magical arrowheads.