IT wasn't stupid, he just overshot his powers. Look what happened in HTTE. When Joruus started controlling the fleet, Palleon noticed it had an incredibly greater margin for success. He noticed everything was going off way too easy, even though it wasn't. The Emperor believed that his powers were more powerful than they really were, and/or he loved controlling them. Either way, when they had that linked severed, it was like finally waking up from an incredibly long sleep. Those people were in complete disarray, most likely because they were in complete shock. They had been controlled for so long, and then they finally just got out from under it. Joruus might not put that effect on them because he isn't as powerful as the emperor was.