Vattel devotees, including those who fancy themselves connoisseurs of the various flavors and gradations of citizenship, might themselves get indigestion from some of Vattel's finest delicacies. The Vattel fetish is for genuine crackpots.
Of course we've never had conscription in this country. And of course we've never had the government to order engineers and scientists to work on various major projects of great interest to our nation. (The Manhattan Project, the Panama Canal, the Hoover Dam, etc.)
You portray what Vattel is saying in bad light because you don't like what he is saying regarding natural born citizenship. You have just created an ad hominem directed at Vattel.
It is axiomatic that the government must hold on to people who have special skills, and not allow them to fall into the hands of our enemies. Our Scientists and Engineers who work in Military weaponry are in this category. They can't just pick up and go whether they like it or not, and if you think this is a crazy idea, you are a fool.
By the way, England did exactly the same thing. During the Industrial revolution, they guarded their mechanical engineers jealously. (These are the people to Whom Vattel is referring.) Fortunately, some of them snuck out and brought their secrets to America, and look how that turned out for England.

;-)
And, you believe that we, as Americans are obliged to slavishly adopt as our own Vattel's other views on citizenship?
Is it your conception of natural law that compels us to look to Vattel for the one and only true theory of citizenship?
It really doesn't get much crazier than this!