China is doing most things right according to endogenous growth theory. Exports help it grow faster but are not the most essential part of the equation. China's export is only ~20% of its 2018 GDP.
https://www.theglobaleconomy.com/china/exports/"Endogenous growth theory holds that investment in human capital, innovation, and knowledge are significant contributors to economic growth."
https://en.wikipedia.org/wiki/Endogenous_growth_theory
> Technology in China is still by and large imported / copied.
For many important technologies, it is either on par, a bit behind, or sometimes a bit ahead (5G, quantum communications) of the west. A few key areas where China still lacks are semiconductors, aviation, and global reaches of internet platforms. These are important but account for far less than half of its GDP.
China's numbers of patents and scientific publications have reached world's no.1 in recent years:
https://en.wikipedia.org/wiki/World_Intellectual_Property_In...
https://en.wikipedia.org/wiki/List_of_countries_by_number_of...
One can argue about the quality of those, but one should not assume that China is substantially behind the west as was the case even a couple decades ago.
China's number of STEM graduates, many of whom are sources of the progress above, is the highest in the world: 4.7m in 2016. The only country that comes close is India.
https://www.statista.com/chart/7913/the-countries-with-the-m...
> ...while Western demand (mostly US, really) and its technology are not.
US population: ~330 million; EU, ~450 million => Total: 780 million. China's population: ~1400 million. Domestic demand is clearly not China's disadvantage.