I've been studying this in more depth today, and my understanding at this point is that the law governing the Cruz situation at his birth was the Naturalization Act of 1952.
That Act required that a child born to an American outside the country would, at the attainment of 18 years of age, be required to swear a loyalty oath to the United States.
This requirement as removed by the 1978 Naturalization Act, before Cruz reached the age of 18.
The point being that the governing law in the case of Cruz has always been our laws concerning naturalization.
Funny, I just went through the entire act, and it does not contain any such requirement.
By definition, the act of naturalization is required because one is not natural born. In any case, a statute cannot override a constitutional requirement. The Constitution can only be changed through the amendment process.