While it is true that China has a lot of 'hands' to add to the production game, it is also true that those additions are at the expense of US (and Mexican) workers.
It is also true that 'productivity growth' has had an impact on the number of workers in manufacturing in the USA. But one can also argue, without fear of contradiction, that PRChina factories have the same machinery and equipment that US factories have.
The only really significant difference is the cost of labor, insofar as tax and regulatory costs NOT related to labor (as heavy as they are here in the USA) are simply not great enough to propel industry offshore.
It's also a helluvalot cheaper to live in PRChina than in the US. Finally, there is the slave-labor component, well-hidden from US eyes. I know a former President of a $250MM US company which was part of a several-tens-of-billions conglomerate based in the Southern US.
That President told me quite frankly that the US Company did NOT pay the PRChina workers. Rather, they gave a check to PRChina, which distributed the money to the workers itself. At least, the US company HOPED that they did, and did so fairly. They don't know, and are not stupid enough to ask.
It is GOOD that we did not "pay the PRC workers." Do you realize what you just said? Their own government continues to be corrupt and starve them---or deny them wages. This is exactly the policy of every 3d world country. When they start paying the workers, worry.