I agree that Congress has the Constitutional authority to create a uniform rule of naturalization.
My question to you is...upon whom is naturalization applied? A citizen or an alien?
Again, does a citizen need naturalization?
Since a positive law (a uniform rule of naturalization or man made law) is required then it can't apply to one who is already a citizen.
Stated another way, your thought process dictates that our natural, inalienable rights don't exist, as they are natural laws, and we need a positive (man made) law to grant such rights.
A “uniform rule” applies to all, citizen and non-citizen.
Under some conditions a citizen can lose their citizenship (title 8 section 1481) even if they are a NBC, and may wish to re-establish citizenship later. They would need to be naturalized.
The “positive law” or Constitutional law can DEFINE who is not a citizen and requires naturalization AS WELL AS, defining those who are citizens and do not need naturalization.
To take this to an extreme hyperbolic example, Congress could pass an act that says that every person born, regardless of location or parentage, who is born with blue eyes, shall be a natural born citizen of the United States. Because of Article I section 8 clause 4, they would be an NBC.