We don't have pure free market economies. Neither in China nor in the USA nor anywhere else. The see big monopolistic companies dominating most markets. We see an closer interlink between state and private corporations.
Even just with the currency manipulation that China engages in, things get screwed a lot. Or the special status the US has with the dollar. Real world is more complicated.
But even if we assume free markets, you misunderstood what the previous poster said. The problem with Ricardo's comparative advantages is that is assumes fixed advantages. It is like optimizing for a local optimum. You might be super inefficient in producing X because you have never done it but if you actually invested in learning how to produce X you might discover that you are really good at it and the comparative advantages would go in your favor.
I do still believe that trading with each others can lead to more net wealth in most cases and obviously full autarky is not realistic these days but like anything in economics, it shouldn't be taken as a dogma.