Note that James C Scott speaks specifically of the very deep pre-historical middle east. I'm not sure if the conclusions are generalizable to China, thousands of years later.

There are examples of large scale public engineering works with and without observable central authority throughout archaeological record around the globe. So just "having walls" is not sufficient implication of central authority attempting to control the population.

IMO in the specific example of Against the grain the central authority thesis is pretty solidly framed. But, it does not aim to be a generalizable theory, nor IMO should it be viewed as such.