Even looking at the entire population, the U.S. has higher reading scores on PISA than the big western european countries (UK, Germany, France, Italy): https://www.oecd.org/en/publications/2019/12/pisa-2018-resul.... In reading, the U.S. was basically tied with Japan and the Scandinavian countries.
That is consistent with other international measurements: https://nces.ed.gov/fastfacts/display.asp?id=1. For example, the U.S. is one of the top performers in the world in the 4th grade literacy--behind Hong Kong but ahead of Macau. In 4th grade math, the U.S. isn't as good, well behind Hong Kong, Singapore, and Japan. But still comfortably ahead of Germany, Italy, Spain, and France.
I read my first Stephen King novel in grade 6. That seems to me more than sufficient aptitude for reading the things an average person needs to read to get through life.
The assignment was to read lots, and lots of 6th graders read Stephen King, because that was the cool thing to do. The size of a typical Stephen King novel is intimidating but the writing is usually straightforward and clear.
That is consistent with other international measurements: https://nces.ed.gov/fastfacts/display.asp?id=1. For example, the U.S. is one of the top performers in the world in the 4th grade literacy--behind Hong Kong but ahead of Macau. In 4th grade math, the U.S. isn't as good, well behind Hong Kong, Singapore, and Japan. But still comfortably ahead of Germany, Italy, Spain, and France.