“What is the difference between a mere “born citizen” (the Founders considered this phrase, but rejected it) and the more restrictive natural born Citizen...”
First, we have no idea what was considered on this clause of the Constitution. There are no records of any debate on this clause. However, Natural Born Subject was a well known legal term used by the Founders often during their colony days, and it simply meant born as a subject.
By restricting Presidents to NBC, they rejected naturalized citizens from the presidency. There were only two categories: Natural born or naturalized. Still are only two.
In the UK they had one sovereign with everyone else being subjects. It suited the UK sovereign's needs to be able to impress "subjects" (such as USA citizens in 1812) into the navy, so the definition of natural born subject was made as loose and all encompassing as possible, the exact opposite of purpose of the definition of natural born Citizen.
In the USA our executive is a public servant who serves his sovereigns, i.e., each and every citizen (exact opposite of the UK system). The natural born Citizen clause is Constitutional job requirement for the presidency (one of three) that was put in place to protect the Republic and its sovereign citizens from foreign intrigue and influence. It makes sense that it would be as restrictive as possible against foreign allegiances in our Commander-in-Chief, the head of our military might. A natural born Citzen must be free of any and all alien allegiance at birth.
You take your RINO new world order BS and get lost.