I mean, it is not weird that India is 40% of Chinese size in GDP PPP
India has same or more population than China, all that population working produces economic output.
Anyway even the GDP PPP does not measure the real size of a economy, GDP was created to track the change in one economy from one year to the next. It can be used to compare economies that are very similar in their structure like lets say Belarus and Russia, or Netherlands and Germany.
You cant use GDP to compare Russia and Germany though, or China and US.
Communist and post communist countries have artificially low GDP due to having free services. Something free does not add nothing to the GDP but obviously contributes to the real economy.
For example in Germany you have to pay medical insurance every month (when you work is paid by the employee but it is still a economic exchange reflected in the GDP, then you go to doctor and the doctor send a bill to the insurance, other economical exchange reflected in the GDP).
In Russia or China (and in some European countries like Spain or Portugal) that system does not exist. The doctors are simply employed by the government and you go there for free. Nothing is reflected in GDP.
In the US 20% of the GDP correspond to medical spends.
This is the reason of why when neoliberals (like Thatcher or Milei) arrive to a country and start to privatize everything (roads, medicine, education...) there is increase in the GDP but often reduction in the real production in the country.
You privatize roads, a new economical exchange appears that is reflected in the GDP. However nothing has been added to the real production of the country, that if something, is now more expensive because transport companies not have to pay to go by the roads.
It exist some level of correlation between GDP and the real economy, but is far looser than most people imagine.
Of course promoting GDP is very useful to push people like Milei to the power, so he privatize things that big investment companies can buy for a penny and then profit from it.
As those big investment companies are owners of all global media they have direct interest in promoting GDP as a measure of success, so people vote idiots like Milei, or support idiots like Gorbachev.
The reason for this is obvious coming from the name, GROSS domestic product. In accounting terms you are just counting income, without counting what you are spending to achieve that result.
If you are in a company, and your gross income is very high, but your spends to achieve that income are also very high you are in a worse position than a company with smaller gross but much smaller spends.
Of course this does not mean that US economy is shitty. US citizens are still the richest ones in the planet. But not so much as the nominal GDP or the per capita GDP in purchasing parity power suggest.
And overall, China being 4 times the US is a much bigger real economy than the US