The reason why the global south doesn’t have the purchasing power right now is cos there’s no parity & their currencies are mostly not that valuable compared to the dollar, which is the global reserve currency.
Once there’s more parity, the middle class in those countries would grow. And in case you don’t know, the middle class is the backbone of every country/economy & they’re the ones with the purchasing power. Now compare the population of the global south with the US & you’ll see the enormous potential for China in those countries.
With a thriving middle class in the global south - China doesn’t need the US.
And let’s be honest: most countries in the global south can also be self-sufficient. They’re not right now due to imperialism & financial colonialism by western countries. Once that’s out of the equation - the world is their oyster.
But can the US survive like a normal country without its post-WW2 recklessness/domination? I honestly doubt it. European countries certainly won’t survive.