There is no proper framework to define a 'developed' or 'developing' country. At the WTO, individual countries are allowed to self-allocate themselves. Those in the 'developing' group then get preferential trade benefits. These trade benefits are the only reasons China holds tightly to the 'developing' country label.

Even if China has the same GDP as US, the per capital GDP will be 1/6. That's the reality. There are cities in China is comparable to western cities, especially infrastructure, because the country has invested a lot in infrastructures. Americans have to know their position. They are not developed world, they are superpower. Below US there are developed world, then developing world, then there are not-developing world (we keep forgetting them).

Personally I believe once a nation reach developed status, the main task for the government will not be generating new source of income and improve people's life financially, it will be about how to distribute wealth fairly.

These labels aren't useful for extremely large / diverse countries.

Coastal China has per capita GDP comparable to Taiwan. Interior provinces is much poorer, with 600M living on 1000RMB/month or 2000USD/year, on the level of Haiti. In aggregate China is a middle income country with per capita GDP of Iraq.

The Chinese system harnesses this income disparity + 1.4 Billion people to concentrate talent, wealth and development systematically rival developed nations. That's just a factor of scale. Quantity has a quality of its own if properly coordinated, which is basically broad TLDR of Chinese history up to industrialization. I suppose people didn't think China could catch up this fast.

China is a US population-worth of developed nation and twice that of developing nation, roughly speaking.