It should be? It should be based on what?
Realism.
That's the problem.
If you were to make a movie (or write a book) where our hero finds himself armed only with a knife against an enemy in full plate armor with sword and shield, you wouldn't have our hero go toe to toe with the armored knight. You'd find some other way for our hero to win -- or run away to come back and win later, or have the demure princess rescue him (oh so amusingly), or bring his attacker to his side, etc.
Action movies and pulp novels don't hold themselves to lofty criteria of perfect reality simulation, but some things make a whole lot more sense than others (or are a whole lot more entertaining), and I'd think a game system should work the same way.
A system that promotes a toe-to-toe combat between our hero with a knife and his Evil-Knight opponent and has them trade blows for dozens of six-second rounds isn't just unrealistic in some strict no-fun sense; it doesn't make for a fun story either -- in part because stories that make more sense resonate better with audiences (and players).
D&D has not been a highly simulationist game, and nor should it be, IMO. By doing so, you move the game away from heroic fantasy and towards an melee infantry simulation.
And anything that makes more sense than the current rules must be less heroic?