What does your (dubious) example have to do with the quality of post-secondary education? If it has any relevance, it's for the quality of secondary education.

I wish it were dubious. I recently worked with 11th grade Algebra 2 students in New Mexico and found exactly that, and worse. Most couldn't begin to do algebra because they couldn't do simple addition and subtraction. Out of a class of 24 there were two who were arguably ready for it. But everyone is moved forward anyway. I understand your skepticism because I was shocked by it. The teachers said it all went down the drain during Covid and has not recovered.

It must severely limit what they can learn in college.

If the college would accept someone like that, they probably don't aim to take their students to a very high level.

If a university's administration overlooks a complete failure of the student selection process, it's easy to imagine that it may well overlook a complete failure of the professor selection process. The price of admission is also way too steep to wind up being the peer of mental 8th graders.