Interesting. There is at least one assumption I question: why is economic growth considered to be a good thing? It's a quibble I have with economics as a whole, though, not his demographic analysis specifically. Given most analysts use growth as a positive measure, it's an enlightening analysis.
"Growth," in heavily financialized terms, is usually a measure of profit. It's important because it looks at how those at the top prosper. However, "growth" in the context of socialist countries like China, a heavily industrialized country, directly corresponds to improvements in quality of life of the majority of society. Productive capacity allows countries to meet more needs, assuming said country is oriented in a worker-focused manner.
Another good way to analyze is based on metrics like life expectancy, home ownership, etc.
I can highly recommend this book for a broad analysis https://redletterspp.com/products/chinas-great-road
The TLDR of it is that economic growth is positively correlated with the increase in the standard of living. A country like China started out with a very low standard of living after the revolution, and the primary goal of the party has been to raise people out of poverty. This necessarily correlates with the rise in consumption.
I agree that you can reach a point where further economic growth may not produce meaningful improvements in the standard of living, but majority of the world is far from that point right now.
