I don't see how DNS MiTM is going to subvert the basic math of public key crypto. Even if the browser is implementing its own SSL stack, it would have access to

I don't see how DNS MiTM is going to subvert the basic math of public key crypto. Even if the browser is implementing its own SSL stack, it would have access to validate those keys against those that ship with the OS. This SSL pinning seems to be something outside the crypto mechanism. It's flair.