Earlier quoted context omitted.
Those areas made far more than they invested, and China needed that huge investment because those three areas had already spent a century exploiting it for profit.
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As for Mao holding back China, no doubt there were big problems. But the greatest increases in life expectancy at birth came under Mao [1] and his push to greatly expand access to medical care and education in rural areas. That was itself an investment which set the stage for future growth. (It's a lot easier to get things done when your people aren't dying at age 45.)
[1] https://data.worldbank.org/indicator/SP.DYN.LE00.IN?location...