The point is that he was NOT addressing the office of the Presidency. Again, President and Vice President are the ONLY offices that demand a natural born citizen. It is required nowhere else.
I addressed your request, “Post a treatise that uses statements from the Founding Fathers that dual citizenship was not a concern.”
I gave you a statement from a founding father on the relative importance of parentage vs. place. James Madison obviously felt that dual citizenship based on the citizenship of a parent did not trump place of birth as the most important criterion of allegiance. That is my point, as a response to your request.