The writer did not have the ability to predict the large influx of cheap labor and the explotation of raw material that surged the U.S. Trade in the late 1890s. That Tarriff actually stymied economic growth for most of the nation, those who benifited from it being a small group of rich men in industrial states like New York and Pennslyvania. The Post Civil War period was highlighted with labor unrest, farmers unions, and a decline in agraculture in places like Kansas. There was growth but it was localized and most of the country did not catch-up for nearly thirty-years. The American international shipping industry was decimated due to the war and did not recover until World War I.
Without the Tarriff the nation may have exceeded Great Britain in trade and manufacturing by the late 1870s. But there are so many variable parameters in determining a nation's economic progresses and declines its very hard to predict.