Is that true? I've heard that the build quality for new houses in China is terrible.

I also keep hearing this. I keep hearing the “American infrastructure is built to last 50-100 years” (I used to regularly pass a handrail at the Wall Street station that was over a hundred years old, so example of one).

But is China’s really so bad it is going to crumble in half of that?

Autocracies have more variability. There were good kings and bad ones. When the tyrant is smart and genuinely lifelong committed to the good of their people you get the most efficient system. This is the classic argument monarchists have. Problem is in reality the planets alignment rarely happened.

Which autocracies were/are efficient? Were East Germany, the USSR, Mussolini's Italy, or Nazi Germany efficient - not sure they were. They could get certain things done, but that is very different from being efficient (or even effective) in broader sense.

UAE, Kuwait, Bahrain, Singapore? I loosely say Autocracies I guess.

All fairly small places... the comparison is then maybe Switzerland, some of the Nordics etc. They all seem to be doing much better in building fast than their larger neighbors.

I agree that a good autocrat can be more effective than a democracy, but also think that bad ones are much worse. Plus autocracies are notoriously bad at picking good rulers/successors, so you end up with a lot more poorly run than well run countries.