What prior languish, happened- in that supposed- 30 year interlude of Red Mao imposition upon the Chinese folks?
The Chinese monarchy collapsed in 1911. From 1911 to 1933, the empire was embroiled in civil war, as some generals attempted to establish their own nation states and others (like Chiang Kai-shek and Mao Tse-tung) attempted to become head honcho of the overall empire. Japan invaded in 1933. The Sino-Japanese War continued until 1945, when the Hiroshima and Nagasaki bombings ended the war. Upon which the Soviets did their version of Lend Lease to the Communist Party (and Soviet agents in the State Department successfully curtailed aid to Nationalists), which overcame the Nationalist Party in 1949. For 30 years until 1979, the Chinese economy was run by central planners who decided where someone worked, what he wore, what he ate, what he drank and where he lived. That ended beginning in 1979. Basically for a 7-decade period beginning in 1911, and ending in 1979, China was either in the midst of all-out war or under the thumb of economic central planners. By comparison, for the same period, Taiwan and Hong Kong were relative oases of peace and economy sanity.
Japan advanced faster because the ancien regime, the Tokugawa Shogunate, was toppled in the mid-19th century, the civil war that ensued was settled relatively quickly, nobody invaded Japan, and the ensuing Meiji government did not attempt to implement Marxist economic central planning there. The Meiji government consolidated its power in 1868 and began opening up the economy to the world. The Communist Party consolidated its power in 1949 and began closing the economy and implementing central economic planning. In addition to China's 80-year lag in terms of basic political stability, the Communist Party tacked on another 30-year lag due to its imposition of utopian Marxist schemes. It's testament to the quality of the raw talent at hand that China's per capita industrial output is in the top half of nations today rather than near the very bottom where it was in 1979.