“Overcapacity” has become the buzzword in Washington and Brussels. American and European policymakers insist China churns out far more steel, electric vehicles and green technology than it can absorb, flooding the world with subsidised goods. Yet the economic data tells a different story: of double standards, protectionist impulses and a habit of moving the goalposts. Start with steel. Western officials point to China’s massive output as proof of distortion. But China official data puts the...