It is even easier to look at India, where the putative democracy the country has has not led to any kind of economic miracle for the poor.
There are a lot of studies about how economic prosperity and democracy/liberalism went hand in hand in a lot of countries. And there are outliers, and the studies can be questioned, and so on.
China rented out its workforce and a relatively enlightened but autocratic leadership made sure it works, they make a lot of money, and that they reinvest that.
India never had such a strong leadership. They probably spent a lot of time and energy just doing what other multi-party democracies do, squibble, play the politics game, and so on.
Also, don't forget how India slowly started to get rid of the caste system and other deep rooted inequality problems, similarly grassroots efforts to curb corruption progressed through the various courts and legislatures.
China spent no time with such sentimental stuff.
You might be interested in: https://en.wikipedia.org/wiki/Cultural_Revolution
China has a full blown caste system via hukous.
I generally agree with you but I think you got timeline wrong. Which matters in this example.
70s in communist countries was a period of relative prosperity. The political repressions ceased, the economies got more consumer oriented, the arms race slowed down, the goverments got more technocratic. Communist countries started to catch up with Western consumption levels. Mass housing developments, car factories, Coca-cola and Pepsi in shops etc.
Lot of younger generation had been happy to join the party not for ideological reasons but for the material prospects it opened.
Then two events happened - first oil crisis and the financial markets dried up suddenly (many communist countries borrowed heavily when money was cheap in eurodollar), second Afganistan, Reagan and Star Wars programme (arms race again).
Communist countries sliped from relative prosperity to austerity which resulted in fall of communism at the end of 80s.
What I am saying is that the revolutions happen often after long period of relative prosperity when economy starts going downhill. And we have similiar circumstances brewing in China right now.
It's more than that.
Back in the 70s, Westerners could very easily make the case that the USSR was corrupt, inefficient, hopelessly backwards and fundamentally organised in the interests of the state rather than the people. The evidence was abundant, even to Soviet citizens; any possible defence of the Soviet system was predicated on blind ideological faith or a tapestry of lies.
Contemporary China is a long way from perfect, but a Chinese citizen could quite legitimately make the case that their system is superior to Western democracy on a pragmatic level. There are hundreds of millions of Chinese people who grew up in squalid shacks with no running water but now have a lifestyle that is recognisably middle class. They're on the tail end of the longest and fastest period of economic growth in human history and they're still growing - we can quibble about the percentages, but their GDP growth figures are still spectacular. While many Westerners are struggling with homelessness due to a chronic shortage of housing, Western newspapers are writing about China facing a crisis due to building too many homes.
We're not talking about North Korea, we're talking about a political system that can be legitimately defended. It's not whataboutery for Chinese people to point out the manifold problems facing many Western democracies right now - there are advantages to democracy, there are advantages to Communism with Chinese Characteristics and there's no prima facie case for the superiority of either that relies solely on pragmatism rather than ideology.
If Westerners want to promote democracy in China, their arguments will need to get a whole lot more sophisticated. Why is political and social liberty really so valuable? Why are the rights of the individual more fundamental than the rights of society as a whole? Why should troublemakers be allowed to destabilize society with impunity? Given the current political climate, finding better answers to those questions might also prove rather valuable domestically.