Going through an industrial revolution has impressive growth effects that can cover up a lot of bad stuff.
We'll see what happens when that growth starts to slow - I don't think it'll be good.
It's not meaningful: Middle class in China would be poor in the US, and developing countries can expand their economies much more quickly.
I am happy for the middle class people in China.
> the best argument free democracies had used to be that the people of those countries were richer and had better lives
You skip the main reason they have better lives, which is freedom. All those Americans (and others) worked and sacrificed for freedom. Wealth is barely mentioned in the founding documents; the Gettysburg Address, FDR, MLK, etc., didn't mention it much (though the latter two did address poverty).
The Chinese 'middle class' standard of medical care ( on average, a lot cheaper but it's also a very basic level of care), financial security, air / water / consumer good safety, access to meaningful education, and freedom of worship / speech / congregation of all types is well under what is typical for a middle class citizen in a western democracy, even including the united states. At around $20,000 USD per year (approx boundary of China's upper middle class) you're in the same general territory as Russia.
When you have observed a colossal material improvement in your life, and you have hope for the future, you can overlook a lot of problems with governance.
[1] Yes, yes, Moscow is not an active disaster zone. Russia does not begin and end in Moscow, though.
It has been long believed to work the other way: Poor people don't have the education or resources to deal with governmance; they are trying to survive, working three jobs (if they can get them), etc. When the middle class expands is typically when democracy blooms.
Russia's 'middle class' expanded massively since the economic disaster of the 90s, but I would not describe it as being more democratic today than it was in 1995.
A rising middle class isn't why communism fell apart in the 80s, either. It fell apart because the country lost any faith that the system will bring future prosperity.
In principle I agree with you, but in practicality something maybe isn't working as expected? If those things mattered so much, why would the Chinese middle class have grown so much while the American middle class shrank? (assuming this is true, which I'm not sure)
At the end of the day, there's still a hierarchy of needs. If one country cannot offer its citizen those needs, reaching for higher level ones doesn't matter. Most people would rather be able to afford food, clothes, a home, electronic, entertainment, etc, than they would the ability to be critical.
On some other dimension, the best argument free democracies had used to be that the people of those countries were richer and had better lives, while totalitarian regimes, religious regimes, communist regimes delivered a worse outcome to its people. And while this is still mostly true, it seems that it's no longer as obvious which one delivers better value to its people.