That is what I have discovered. In the English vernacular of 1776, the word "Citizen" meant dweller in a City. The English usage of the word at that time did not encompass a member of a Nation-State.
It did however do this in Switzerland, which was a confederated Republic at the time.
The argument that I have recently decided is most compelling is this:
That the founders insisted on using the word "Citizen" means we got it's meaning from Vattel, and not England. Had they intended it's meaning to flow from English Common law, they would have kept the word "Subject."
The very word "Citizen" requires Vattel as the source, and not English common law, because the English didn't even use the word in that context.
That the founders insisted on using the word “Citizen” means we got it’s meaning from Vattel....”
No, because the direct American experience with the usage of citizenship to denote urban and/or national citizenship long predates the birth of Emer de Vattel. Vattel’s works only restated what the North American colonists had been personally acquainted with since the founding of the Jamestown and Plymouth Colonies through their contacts with other Europeans in Europe and in the Americas. In particular, one of the huge influences upon the Founders was the Dutch Republic and its former colony in North America, the 17th Century Colony of New Amsterdam. See for example:
New Amsterdam - Notable Citizens
https://www.geni.com/projects/New-Amsterdam-Notable-Citizens/5376