It’s worth noting while their speed is impressive and admirable, there’s a major issue plaguing their construction - poor quality. A lot of work is done poorly and there is often corruption involved in the process. More often than not, durability and quality are overlooked for the sake of speed.
There’s a lot of media coverage of the poor quality.
https://www.wsj.com/articles/china-global-mega-projects-infrastructure-falling-apart-11674166180
There’s even a term for poor-quality work in China.
Overall, while high speed is great and I wish the US could have faster construction, it’s better to have a project that’s high quality, built properly and will last. That second part - quality and built properly cannot be said for a large number of China’s big infrastructure projects. It’s all about speed and showing “look what we can do” without regard to whether or not it’ll last into the next decade.