Iron Troops as China are really fun but they feel like they fall off super hard later. Maybe add a buff similar to European civs for mercenary attack/hp when going to imperial? That could also be a shipment similar to German mercenary camps just for China to buff maybe Manchu plus iron troop?
Or at the very least buff the monastery wagon shipment to increase the build limit of monasteries. I think that having only one building train so slowly really stops them from being too good late. Build limit feels like it would be more useful than just pure train speed but that is the other option to actually build enough to make them viable. Most other Civs have some level of tavern build limit increases so why not Asian civs also?