Koon can't hit him with his lightsaber and Haazan has lightning that can kill multiple Jedi at once as well as telepathy able to make powerful Jedi like Lucien Draay do his bidding. As well as mastery of sorcery which I doubt Koon has much experience with. Plus he's not too shabby with a lightsaber, killing a 3 man Jedi strike team with ease.