China has high GDP because China has the population to work for in full employment. China had relatively the same population of the Continent of Europe in 1900. Before then China was larger than Europe. China is a continent, united in one country. That is China's strength.
With Europe's modernity and birth control and reduced population is some places. Europe is 750M. Europe chose stagnation. And is taking in migrants to help with their population woes. China continued to grow and is the largest economy because of her population. If you are of the mind-set that population bring woes, how can you figure out a policy of a consumer driven Chinese economy, since that would collapse the economy if Chinese turned to a high consumer economy because too many people = burden and trouble.
China = Europe. China area size is almost the size of Europe. I repeat, China is a united continent as one country. China is like the Roman Empire continuing for thousands of years. China should have a high population. China falling to half the population of Europe for zero population growth and to lessen burdens on CCP, means CCP is useless.
China can make 1000s of subs and 1000s of frigates and warships because of China's high population. China is a continent. Don't limit China as some country comparable to Sweden. Sweden is limited due to low population in making a large fleet.
Machines making machines does not limit prosperity. If a 7 million population country can make AI robots to make life easy for 7 million. A 1.4 billion population country can make enough robots to make life easy for 1.4 billion. Limited resources limit AI machines making machines. Which is why I advise China to stockpile 100 years or more of raw materials like iron and steel, and other metals, so China can survive not only sanctions and war, China can survive shortages of raw materials used for development and quality of life, and military defense. This is why Australia exporting iron ore, makes me happy. Places like US should be stripped of rare earths to the global supply chain. Australia should run out of ore before the free world of China runs out. Use up their resources, don't use up China's resources, and if you need to, import even more iron ore and stockpile, don't dump steel on the US wasting money and steel. Raw materials are the most important thing, other than tech, in that future of AI, and machines serving citizens, of robots and driverless cars.
I seek ways to prepare China for a future of limited resources. If you want the population of China to be 300 million, you are not preparing for 1.4 billion with a vibrant economy and enough resources. You are simply blaming too many people and the need for zero children and a bright future of a few million Chinese enjoying the fruits of a future economy.