You are ignoring the rest of what Madison said. Madison said it was a general principle, but he also said that had South Carolina had a law explicitly stating what a citizen was, then it would have solved the whole problem before it got to the House of Representatives. Also, the issue was a matter of STATE citizenship, not Federal.
Beyond that, when Madison was President, he deliberately let the French Hold James McClure for a year and a half because a birth certificate from South Carolina wasn't sufficient proof of citizenship. You can talk about what Madison said, but what he did speaks far louder.
If I have misunderstood your position, I apologize. But if I was right, and you're still giving Vattel's opinions more weight than Madison's, it was no straw man.
You are falsely attributing that one sentence by Madison as being all encompassing and not considering it within the context of the rest of what he said. You are interpreting it as an Absolute as applied to Federal citizenship when it is a "general principle" and is being applied to state citizenship in a state which does not have a specific law to the contrary.
Madison also invokes William Smith's Jus Sanguinus claim in his very next sentence in which he says:
Mr. Smith founds his claim upon his birthright; his ancestors were among the first settlers of that colony.
William Loughton Smith:
"The Doctor says the circumstance of birth does not make a citizen-This I also deny. Vattel says, "The country of the father is that of the children, and these become citizens merely by their tacit consent." I was born a Carolinian, and I defy the Doctor with all his ingenuity, arithmetical or political, to say at what moment I was disfranchised- at what moment I lost my citizenship."
I have more evidence that Madison was not in Conflict with Vattel, but there is too much of it to post in one message.