This is a weak argument. The US has a patchy K-12 system whose quality varies from abysmal to world-beating, depending on many factors. It has, indisputably, one of the world's best universities. Lots of people who have gone through the former but are also products of the latter. They can be very well educated, and do better than credentialed teachers (let's face it, the only difference is that; also a known fact that brighter, higher-IQ people do not gravitate toward K-12 teaching).