I don’t accept that the definition of “B” (subject) is dispositive in defining “A” (natural born citizen).
The Supreme Court decision that I believe you are referring to is Minor v. Happersett, which to my knowledge is the only one to have defined “natural born citizen”. If this is part of the holding, as has been asserted, and not dictum, then it would be dispositive in construing the term “natural born citizen”.
I don’t see how the 14th amendment amended the definition of “natural born citizen”, since the term “natural born citizen” was not used in the 14th amendment. I do note that the Citizenship Act of 1790 extended the status of “natural born citizen” to people both of whose parents were US citizens, even if those people were born at sea or outside of the US. That law was superceded by the Naturalization Act of 1795, which did not use the term “natural born citizen”. However, one could use the 1790 act to argue that congress, in promulgating that law, understood that a “natural born citizen” had to have two parents who were citizens (unless born before the US was organized).
My point about the 14th is that it redefined who was a US citizen. Therefore a Court decision is needed to determine whether it made any difference in who was NBC.
But that is perhaps irrelevant since the original definition of NBC has not been defined.
I do find it significant that in the Wong Kim Ark decision the Court quote Blackstone extensively and referenced common law as the basic principles applying to US citizenship. If I remember correctly, one of the dissenting opinions stated that he was dissenting partially because otherwise “coolies” would be eligible to become president, at least implying that he would be NBC.
It is relevant that not only was neither of Wong Kim Ark’s parents citizens, as natives of China they were at the time not capable of being naturalized.
BTW, I agree none of this is dispositive. Which is why we need a Court decision.