If the Gangplank is really good at managing his barrels it does make the matchup harder, but it doesn't make it one of the worst. What ends up happening is that he chunks you bit by bit until he can all in. Kled still has the advantage in lane as long as he doesn't get chunked by barrels and Q from Gangplank. And of course, a challenger Gangplank will most likely play against a high elo opponent who will respect the barrels.