So being "Property" and being "discussed in WKA" explains why they meet the requirements of having been "born here" but were not citizens?
I'm sorry, but that is just fluff and nonsense. "If they were "natural born" before the 14th amendment, then they were "natural born" after the 14th amendment. The Condition of being "natural born" cannot be changed by statute.
The only reasonable explanation is that neither Indians nor Slaves were considered "natural born citizens" prior to the 14th Amendment,(or after. Note use of the term "citizen" in the 14th amendment?) and Indians weren't considered "citizens" until after the Indian citizenship act of 1924.
Nor by any other law made by political process, such as a Constitutional Amendment.
A natural citizen is such by natural law, and not for any other reason. Natural law defines what is true by the nature of the world, regardless of what any political entity may decree. So the 14th Amendment cannot have changed who was or was not a natural citizen. It's text makes no claim that it does.
To see who the natural citizens are, remove all the laws and Constitutional definitions regarding citizenship. Whoever are still citizens must be so naturally, by the nature of things. Any such who weren't so from birth—such as those who became citizens at the moment the nation came into existence, without needing any statute or Constitutional provision—are natural citizens. Any who were such from birth are also natural born citizens.
By definition of natural and born.