That is why I mentioned they still have a significant room for further development. (Many people's quality of life in major cities, from all reports I have seen, is no worse than that of the west's middle class, except for pollution.)
If a country is economically well-governed and still developing, the quality of life for most everyone will improve over time.
Most people who have studied or traveled to one of the Asian tigers before and after its rapid phase of development can see how different 2-3 decades can make.
A 5% annual compound growth results in 3.4 times the previous GDP within 25 years.
2020 projection of GDP per capita (PPP) of China is ~$21000 according to the IMF. It's a middle-income country. If they continue to adopt and invent technologies extensively, there is no reason they cannot grow further.
https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(PPP)...
Quality of life is not a zero-sum game. In fact, when a country is richer, their trading partners are often better off too.