Well of course, when they fail to give sound legal footing to such a rejection, it is a letdown to the rule of law. You should not only be disappointed but angry.
I would be more sympathetic to the idea if you could show some recent articles (say past 50 years) that showed the widespread acceptance in the legal community of Vattel as a key influence on current US citizen laws.
Your premise is flawed. NBC is a Constitutional term that is separate from "current U.S. citizen laws." You do understand that right?? The SCOTUS said, "In Minor v. Happersett, Chief Justice Waite, when construing, in behalf of the court, the very provision of the Fourteenth Amendment now in question, said: "The Constitution does not, in words, say who shall be natural-born citizens."" Statutory law cannot change that which is defined outside of our Constitution. And you err in your thinking, because the legal precedent in Minor is not attributed to Vattel, but it is "the nomenclature of which the framers of the Constitution were familiar." Current laws and current legal cases won't change this. It would require a Constitutional amendment.
Vattel was trotted out only when people started looking for a reason to challenge Obama’s eligibility.
It is what it is. The SCOTUS said this was the nomenclature of which the framers were familiar. If that excludes Obama, so be it. Vattel is simply recognized as an authority, and his definition is very succinct. But we don't need it thanks to the Minor definition. Nothing trumps that.
Statutory law cannot change that which is defined in our Constitution. What's defined outside the Constitution is going to be a subject of disagreement, and all sorts of evidence enter into the debate.