Once Kirito stopped being dumb, he realized the pistol could be used as a second "sword" (which he had done previously in the knockout rounds prior to the main tournament).

It wasn't a bad visual effect here. As deathgun started to go invisible, kirito "stabbed" him with the his "second sword."

That said, I wonder how well the lightsaber functions in the way Kirito is used to, very heavy blades. Since it didn't look like he was batting aside the estoc very well, I would wager that Kirito was at a severe disadvantage that whole fight.

So no, there is not suddenly a better swordsman. Deathgun had been playing GGO for two years while Kirito was off farting around in ALO with his harem. He had all the good gear, and Kirito bought whatever he could last minute and barely knew how to play.