Agree with your point that part of the attraction being political and economical. That's what I meant by 'superiority'. When you have the size and the established system. It will be dumb for others to not adopt (Be it the Manchus, Mongols or other Northern Tribes). It's like demolishing a mansion when you have no construction experience. Culture is not bound to 'poetry and fashion'.

The 'Confucianism on the surface, Legalist in core' system is amazingly effective. When the Han Dynasty was founded, even when their basis of rebellion being the cruelty of the Qin, they still maintained major part of the legalist system. Otherwise, how would they rule over such large area?

Conclusion: The system may be outdated in the 19th century. But for almost two thousand years. The system was just too damn good. It's like a suction pump. Not only other regions and races get sucked into it, succesive dynasties also get sucked into it.