Well yes, you could say that both sides benefited since China was allowed to develop, while the US consumer was allowed to buy cheaper goods. In terms of power, however, the exchange has been entirely in China's favor. As a result of this free trade policy, China transformed from a more or less agricultural society into a industrialized, technologically advanced nation, and an economic and military superpower. The USA is faced with a declining industry, a destabilized society, and its most dangerous rival since the war of 1812.
Also, your notion that tariffs always backfire fore the nation that imposes them is simply wrong. The USA used tariffs in the 19th century to protect its own emerging industry against British competition, and that worked out pretty well; there are more such examples of successful protectionism, such as Bismarck's Germany and Cromwell's England.