To refute this, we either have to come up with a way of measuring whether streaming students based on their scores is a benefit, or we have to come clean and say it's arbitrary.
Saying that high school doesn't teach you anything vocational but you learn how to learn is interesting, but to answer the OP directly we need some evidence showing that students are indeed learning to learn. Otherwise, it's just faith.
We should be especially wary of survivor bias hre. Most folks here are educated and pleased with their career arc. It's easy to assume from n=1 that our education is the reason. But many who took the same classes aren't doing so well. Maybe our education isn't the reason for our success.
One criticism of IQ tests is that they measure the ability to pass IQ tests. Do we have the data to refute the accusation that standardized tests measure only the ability to pass standardized tests?