I think that the two problems are that:
- A) The Asian trade is backward, and that most realistically Beijing should be the end node of trade, since all the worlds silver tended to be drawn to China.
- B) The way you profit from trade should be different, the "collecting" should be removed, and you should just get profit from your share of the amount of trade that goes through your node.
So, something like this:
China provides manufacturing goods. These goods flow out from China according to the development in the rest of the world - reduced by the amount of manufactories in the rest of the world. Each time a set value of goods flow through a trade node, they add trade profit to the node, that are distributed according to the trade value among individual nations there.
If the rest of the world builds too many manufactories, China's income and mandate tanks. This would also mean that late-game, the biggest profit should shift from trade to production.