Eh, I think both you and the poster below are making a mistake in using the population of the city center of Detroit. The city center is making a bit of a comeback, but the majority of the population lives in the surrounding metro area, which still has a population of roughly 3.7 million.
And before you complain about that being a much bigger area, here's the land area for metro Detroit compared to some of China's biggest cities:
Detroit metro: 1,337.1 sq mi
Guangzhou Urban: 1,483.95 sq mi / ~11 million
Shanghai Urban: 1,550 sq mi / ~24 million
Chengdu Urban: 1,760.0 sq mi / ~11 million
Chinese cities typically have boundaries roughly equivalent to US metro areas. They certainly have larger populations than Detroit, but not as much as you guys think.
[1]https://en.wikipedia.org/wiki/Metro_Detroit
[2]https://en.wikipedia.org/wiki/Guangzhou