Are China’s integrated supply chains inefficient?

I've read lots of commentators mention China's vertical integration, from commodity extraction to finished good, as a major economic strength. But conventional wisdom makes me expect that it's more efficient to import commodities and simple secondary goods from poorer/cheaper markets, while specializing in the high-value-added part of the value chain.

So is China's supply chain integration actually more efficient than I understand? Are they intentionally being inefficient? What's going on here?