Well said. I've read the references to the Federalist Papers, English common law, etc., etc. But the first sentence of your post simply makes the most sense of all.
So if a person, by reason of birth, can be both a US and a Canadian citizen, he - by my thinking - is not natural born. But I am not I constitutional lawyer, just a citizen who prefers plain thinking. So I freely admit that I might be wrong.
“So if a person, by reason of birth, can be both a US and a Canadian citizen, he - by my thinking - is not natural born.”
Which in your reasoning would also apply to all anchor babies, since in almost all cases, even though born in the United States, are also considered citizens in the parents’ native country. Mexico considers anchor babies also Mexican citizens.
That concept is known as "common sense" It is attributed to British commoners, and describes the same sort of skepticism expressed by the King's subjects when the ruling class tried to pull a fast one on them.