Been thinking about it, and I like the idea of the fighter being the paragon of the mundane. But instead of this being about him as an apt user of mundane weaponry, why not have it be about him being so ungodly ground in the mundane world that every weapon he uses becomes mundane, every enemy he strikes loses part of it's magic, ever magical weapon that is brought down against him turns mundane as it strikes his armor?

Level 1: A fairly apt soldier, trained in many styles with many weapons. Far more than conscripted militia, yet not worth writing about.

Level 5: Amazing soldier, capable of turning the tides of an entire mundane battle by shear virtue of his training, strength, and any other applicable stats you've not dumped. Might swing a magical sword, doesn't really think twice about it being magical but still benefits entirely.

Level 10: Starting to become so grounded in the material plane that magical abilities stop affecting him. Gains SR, magical touch attacks stop counting as touch attacks and instead become slightly more mundane around him.
Blocks spells as though they were just mundane means of dealing damage. Treats mage armor as he would any other armor not made of metal, leather, or even cloth. I.E. doesn't even notice it's there.

Level 15: His grounding in the material world starts affecting those around him. Higher SR, maybe antimagic sphere x/day. His attacks also carry some portion of this grounding with them.
Dragon flying overhead using supernatural flight? He knocks an arrow, aims, and fires it with such conviction in the laws of physics and the material plane (Without ever even realizing this, it's more of just him having such a strong idea as to what makes sense, action/reaction), that it takes flight carrying this conviction with it. Although the arrow hits the dragon with little more force than is necessary for it to even know anything happened, this conviction strips it's magical flight and sends it plummeting earthward. Shocked, it attempts to breath and merely manages a to... breath. While the smell of a carnivores breath might be horrible, it doesn't exactly deal any damage to him.
Magical arms and armor around him lose their abilities, flaming swords are extinguished etc. Long enough exposure wipes them out permanently.
Cleaves through your magical defenses with every blow causing them to backlash in your face, walks through force walls and they collapse under the power of the material plane.

Level 20: Magic isn't even a thing he realizes exists anymore. All of those magical weapons he was sold as a youth must have been scams. Antimagic sphere at will, except not really at will, just manages to appear when he encounters something that he knows cannot be.
Walks into a magic shop, is shown an epic artifact sword, picks it up, comments on how brittle and dull it is. Shop keeper is horrified that his +5 keen vorpal flaming sword is now worthless. Shouts, tells the fighter to leave, attempts a volley from a magical repeating crossbow. A single arrow lamely flops out onto the ground in front of him as the magic that powers it is disrupted forever.

At level 20 he could easily take a 20 wizard on, given enough surprise and enough planning. The wizard could also take him, though. Most likely both are sitting in their castles with their retainers, unwilling to risk life/limb to go after the other.

tl;dr By level 5 he is as good as you can get in tripping/disarming/bull rushing/grappling and fighting with a few weapons standard to his unit/school or whatever fluff you wish to use.

Level 10-Spell resistance

Level 15-Disrupts magic with his attacks, magical effects falter around him.

Level 20-Manifested force of the material plane waging war against the interference of outside/arcane/divine forces. Uses mundane weapons only, as they are the only kind that exist in his mind and in his world. If you can't take him with a mundane means, then you'd better kill him in his sleep.