According to accepted, widely known history books written prior to 2007, who is recorded as being the last President under the grandfather clause, and who is recorded as being the first natural born President, Mr. Rogers?
You're lawyering and creating plausible motivation and it works to a point, then you collide with recorded history.
You just did.
We never had a ‘grandfathered’ President, since they all were born in the USA or original colonies. Remember, the clause allowed ANYONE WHO WAS A CITIZEN at the time the Constitution was adopted to become President. CITIZEN includes naturalized citizens.
There was no need for a grandfather clause for Washington. All who were natural born subjects became natural born citizens automatically, with the treaty signed in 1783 although US courts held the date to be 4 July 1776.
This isn’t open for dispute. It was involved in multiple inheritance cases. I’m sorry you have believed otherwise, but no court from early America agreed with you. You are completely wrong on the facts.