His winning that fight actually made sense, though. He won by cunning and guile, not brute strength. Shran was going all out trying to kill Archer, because that's how the ushaan works and that's just the kind of guy Shran was. Archer found a loophole and did all he could to stay in the fight (I think it was pretty clear that Shran would have eventually killed Archer) until he could get into an advantageous position and disable Shran.One of my least favorite Archer moments was when after 3 seasons of him getting his ass kicked they have him win the one fight he should of lost against Shran. Instead of Shran losing an antennae the fight should have ended with Archer losing an eye.
But the fact that a man who had never trained with that weapon was able to beat a man who had trained with it for his entire life was way beyond the suspension of disbelief IMO.