According to history, the fall of Xiangyang is caused by two siege machines built by Arabs. The Xiangyang's sister city Fancheng fell earlier because of the catapults which can lob 200+ pound stones, destroying anything it hits. Both apparently Fancheng and Xiangyang lasted for only days each. The city of Fancheng was slaughtered, while Xiangyang's populace was saved due to General Lui's surrender.
You'd think the clever Huang Rong might actually come up with a clever strategy to counter those catapults or at least Gwok Jing might lead a force of elite fighters + soldiers to kill their way to destroy those things or at least assassinate the Arab engineers. But I guess they didn't.
How would've they cope with the siege machines?