Naruto until he went four-tails, and it wasn't easy for Oro to survive the fight that followed. He was absolutely sure the Third had nothing that could cause him trouble, but he did. In the end, Sarutobi rendered his arms useless for quite some time. So maybe Oro is convinced he is prepared, but it's entirely possible that these four have something up their sleeve he doesn't know about. Wouldn't be the first time.