Do you really think that the average intelligence/education level would be higher if we just didn't have schools?

Maybe you're an autodidact like many other engineers, and maybe you would have done better without schooling. Such people are a minority.

Like many, I think you're confusing "the school system is flawed" (it is) with "school bad."

It could though, right? Like let's assume vouchers lead to much better school outcomes. Those would still have to be funded by taxpayers.