2. The Fighter Draws on Training and Experience, not Magic
Fighters master mundane tactics and weapon skills. They don’t need spells or some sort of external source of magical power to succeed. Fighters do stuff that is within the limits of mundane mortals. They don’t reverse gravity or shoot beams of energy.
3. The Fighter Exists in a World of Myth, Fantasy, and Legend
Keeping in mind the point above, we also have to remember that while the fighter draws on mundane talent, we’re talking about mundane within the context of a mythical, fantasy setting. Beowulf slew Grendel by tearing his arm off. He later killed a dragon almost singlehandedly. Roland slew or gravely injured four hundred Saracens in a single battle. In the world of D&D, a skilled fighter is a one-person army. You can expect fighters to do fairly mundane things with weapons, but with such overwhelming skill that none can hope to stand against them.