He's distracted very easily by the very large spider that appears out of nowhere, and centuries of bias don't disappear in a few moments. Especially as it shoots web, and he's learned what that can do. Between that and the firebees (what is Thedas, he doesn't know) the Venatori with the creeping realization he's losing gets an up on him enough to throw a person at Thranduil- points for creativity- and all he can do is bring his swords up and duck, hoping to shatter the man. All hope of rolling away has been ruined by the webbing and the acid.