No one is saying there isn't, but it's objectively a stupid massive oversimplification of how complex things like a human brain and human learning really are.

For one, people used to be a lot better, do unless you think people are actively dumber, you argument doesn't hold.

School capabilities also correlates massively with things like access to resources and wealth of parents, and inversely with mental health.

We also have very strong incentives as a society, as an economy and as a democracy to have as many educated people as possible, to work on setting the best conditions possible for people to learn