The Supreme Court DID rule on the matter of Ted Cruz's citizenship in the guise of Aldo Mario Bellei. He and Ted Cruz share the exact same circumstance of birth. They were both born in foreign countries to American mothers and foreign fathers.
The Supreme court ruled that Bellei could be stripped of his citizenship because he did not comply with the requirements of the law which granted it; The Citizenship act of 1934. (and subsequent modifications thereof.)
How can you argue that someone who could have been stripped of citizenship is the same thing as a "natural born citizen"?
It can also be argued that he wasn't stripped of his natural-born citizen status, he relinquished that citizenship. He knew what was involved in retaining his citizenship. He didn't do it. He lost it through his own actions.