I am not even slightly surprised. I see the same fallacy reasoning repeated in these threads. Much ignorance out there.
You've been researching this issue for quite awhile too. Within this last year, I came up with a theory that the usage of the word "citizen" betrays it's origins and meaning.
Where did they get the idea to start calling themselves "citizens"? If you read Shakespeare or Blackstone, you find the term used to describe the inhabitants of a city. "Denizens" of a City. "City-Zens."
The usage of the word to describe member of a large nation does not appear to be common place in 1776. The word "citizen" is however used in a very influential treatise of that period.
Chapter 19, Title in French: "Des citoyens et naturels"
"Les citoyens sont les membres de la societe civile : lies a cette societe par certains devoirs et soumis a son autorite, ils participent avec egalite a ses avantages."
I am thinking that the word "citizen" is itself proof that the origin of it's usage by our nation is Vattel.
Again, the normal and usual word up till that time was "subject." Using the word "citizen" appears to be an inspiration, and a deliberate break from the character of a "subject."
The constitution says what it says - it was thoughtfully composed. One can look to the Articles of Confederation as the direct predecessor. Citizenship in the union followed citizenship in the states, and under the constitution, states were precluded from naturalizing people into the union - that was left for Congress.
I think you are right on the history or usage of the word "citizens." The founders inverted the power pyramid, and "subjects" would have been anathema to them. The subjects became the king, and the king was subservient to the subjects.