I hate to rain on y'all's parade, but the US measure of literacy is much more stringent than China's. America is counting literacy as the ability to use print materials like brochures and manuals fluently, the rest of the world just bases literacy on the ability to read a handful of test sentences in a controlled testing context. That's the reason that America appears to have gone down as well, they switched literacy measures. The 79% measure is people who are "at or below level 1 literacy", meaning it counts people who met level 1, people who didn't meet level 1, and people who couldn't even take the test at all because of a language barrier or disability. https://nces.ed.gov/pubs2019/2019179.pdf

I'm all for dunking on America but the apples to apples here would be comparing America's 96% (just excluding those below level 1) to China's 97%. Historical materialism requires a true material basis to work.