The headlines grabbed attention: “China’s economy grows at slowest rate in nearly 30 years,” noted the Financial Times in a typical example. China’s GDP growth in the second quarter had slowed to 6.2%, the smallest gain since 1992, back when the country’s economy was first shifting into high gear. But the recent drop was not such a big fall from the 6.4% GDP growth rate of the first quarter, nor from the 6.6% rate for all of 2018. The big picture shows that China’s GDP has been falling for a number of years and the new number is just the latest in a series. And while some analysts were connecting the sluggish growth figure directly to the current trade spat with the U.S., that’s not the central problem, according to experts from Wharton and Stanford University. Rather, the challenges to China’s economy are deeper, structural, longer term, and have been building for years. They include over-investment, high savings and modest, if growing, consumer spending, high debt and low industrial productivity.…