The librarian gave master chief the ability to win. That's the only reason he won. Here's an actual quote: MC: "Can I beat the Didact without it?" Librarian: "No." Plus, you need to catch up on your lore. Chief was 12-16 at the beginning of the Human-covenant war. Halo 4 takes place years after it ended. This shows how little you know about the lore. We haven't even started talking about the precursors yet. Forerunners would win, but precursors would utterly stomp.