Thomas Piketty writing in his book Capital in the 21st Century examined the economic history and growth rates over time of several nations and found that the economy of nations stabilize when mature at a fairly modest, low rate in comparison to the rapid growth rate of developing nations taking up the technology and economic tools of more advanced nations. It is thus reasonable that the Asian nations have a faster rate of growth than those of the west. Eventually they too will stabilize at the same level as those of the west I would think, or might if several externalities such as limits to population and resource growth or ecospheric challenges do not arise to change things.
Sustaining high rates of growth for several generations is improbable because of the compound nature of the increase. Doubling a population or rate of growth every few years instead of over several generations would quickly deplete planetary natural resources.
One might regard the west coast of the United States as being in decline compared to the east coast because Democrats have taken over largely, yet that isn’t the sort of answer some would be looking for. Decline is an ambiguous term since there are so many possible value systems to choose from. If one wonders about civil liberties the west still has more than nations like China, yet for decadence socially the west might have more of that than the orient.
If one is looking for zero population growth and a sustainable ecological economic based economic reform with free enterprise working within a directed political economy with a goal of restoring the vitality of the world ecosphere in my opinion East and West are equally in decline.