>There isn't any reason to think the average Chinese person will permanently keep producing 1/6th as much value as the average American

It's entirely possible given how the current Chinese government has forsaken its previous commitment to economic liberalisation and is moving towards more and more state control of the economy. If it moved close enough to the approach of Maoist China (or current North Korea), it could go decades without seeing any meaningful growth in GDP per capita, much as North Korea doesn't see any significant GDP growth.