In history the Chinese were famous for their siege weapons. The Mongols literally captured Chinese engineers to learn more about siege equipment to help them lay siege to Chinese walled cities. It’s silly for the Chinese to have mediocre siege. At least allow them to research siege engineers, if not for free. Yes, free siege engineers. If this is too strong, give them another bonus for siege. Rocketry helps their scorpions, but that takes ages to tech into it.
As it stands, Chinese are bottom tier for low elo players, free siege engineers will at least give them a powerspike for low elo players. The Chinese are only good among the very high pro elo players, which is less than 1% of the playerbase.
If not buffing siege, give them some sort other buff so they can be at least more playable for lower elo players.
If somehow, this has no effect. Just make it start in castle age. Now, the Chinese have terrifying siege weapons in the castle age. Their onagers, scorpions will have plus 1 range due to this. And their rams will be stronger.