OP, you may have simply encountered a Mount & Blade god. And I don't mean that in a mocking sense either. There are some players out there who are so skilled they are near-impossible to beat without closely coordinated teamwork. There cav players who can hit a bump-stab almost 100% of the time, and archers who can judge distance, timing, and missile trajectory better than any aimbot.
It's part of the beauty of M&B multiplayer. The learning curve is as steep as the Matterhorn, and the skill ceiling reaches far beyond the heavens.