Then here is how I would answer your problem:
The grandfather clause is, I guess “or a Citizen of the United States, at the time of the Adoption of this Constitution”. That means that a NATURALIZED citizen, having probably fought for the new country during the Revolution, could become President.
There was an example, although I don’t remember the name. He came to the US in the 1760s, fought in the Revolution, and then was for a time Speaker of the House. As a naturalized citizen, he would ordinarily been prohibited from being in line to take the Presidency, but he was a citizen at the time the Constitution was adopted.
It also allowed anyone born outside the USA, who was a naturalized citizen in 1787, to become President. And again, I think there were two motivations for that. Politically, it made a lot of folks figure THEY could become President, and thus they voted for it. And second, most of those would have fought in the Revolution and thereby proven both their understanding of the new country, and their devotion to it. Those who helped deliver the new country shouldn’t have been barred from the Presidency due to being naturalized citizens, and they were not.
The point of any grandfather clause is the sunset effect. Once all who lived at the time the Constitution was adopted died off, the only remaining criteria would be NBC status. So I am not sure how to read your response. The clause creates two distinct categories of qualified individuals, one of which would expire over time (”US Citizen at a specific time”), the other remaining for perpetuity (NBC). It does not specify naturalized versus “born here,” but creates this temporary transitional category for all who are not NBC but are still a citizen by whatever other means then allowed, whether by naturalization or by birth. Again, that second category is gone now. It cannot be used to directly define modern eligibility. It can be used to explain many of the early exceptions to NBC qualification, such as Jefferson. Hence my uncertainty in evaluating your response.
I've encountered your peculiar insistence that the United States was somehow just a continuance of English rule many times over the past four going on five years, and this has got to be the strangest by far. “Naturalization” had nothing to do with the so-called “grandfather clause.” The Founders grandfathered themselves and their generation because they could not be natural born. They could not be natural born because the country didn't exist when they were born, your strained assertions to the contrary notwithstanding.
At least three delegates to the Constitutional Convention (Alexander Hamilton, Robert Morris, and James Wilson) were not born in the US but were citizens at the time of the adoption of the Constitution. They did not need to be naturalized because they had been born British subjects and were living in the US at the time of the Declaration of Independence.