NBC is a legal term of art. It's not expounded in the constitution, and while a statute could express what NBC is, what NBC is does not depend on the existence of a statute. Same goes for "citizen" other that of the naturalized sort.
I agree with your conclusions, but the text of the 14th amendment doesn't get us there. IIRC, it was said that the 14th amendment has ZERO effect on the meaning of NBC. The 14th amendment operates to prevent states from excluding people (slaves, mostly) from US citizenship.
“I guess my point is that you could take 301(a)(1) out of there. Citizenship to us-born would still attach by the 14th amendment, and not depend on a statute, like Cruz’s does.”
No, because you are missing how the purpose of Sec. 301(a)(1) is to serve as the statute that implements the imperative or mandate of the 14th Amendment. In other words, just as the Constitution enumerates the power for the Congress “To establish a uniform Rule of Naturalization”, that Rule of Naturalization is embodied within the U.S. Code Title 8 statutes. Likewise, the 14th Amendment to the Constitution also implements its mandate in the same Rule of Naturalization embodied within the U.S. Code Title 8 statutes.
“NBC is a legal term of art. It’s not expounded in the constitution,”
It is not supposed to be “expounded in the Constitution”, because it is natural law already expounded upon in millennia of common law traditions and acted upon in the courts of law relying upon common law judgments and case law.