Average salary in China isn't super low anymore (about 17k USD a year), average wage in China is far better than the US in terms of COL. In terms of COL, average salary in China works out to about $94,000 USD, which is pretty much exactly what the average job would be earning in the US if jobs kept pace with output and inflation.
The fact that the UN and WTO still gives China developing nation status is an absolute joke. They whine endlessly about pollution but do nothing to put the brakes on the most polluting country of all, because all those bureaucrats are making money hand over fist with personal investment in China. If they actually cared about the environment they'd place regulations on China's pollution which would directly effect their economy to benefit the US/West and give the US/West ability to start building up their middle class again.