The point is that no one is a citizen before they are born.
That's an observation, not a point.
Show me any evidence...
How about your own words?
This may be either through being born in the land or being born to a parent who is a citizen, according to the applicable law of naturalization enacted by Congress which is within its Constitutional purview.
...who become citizens later through a process determined by Congress...
Isn't "at birth" when you said it happened? Congress says it is. Your words indicate it is as well. Why do it later?
You want your cake and to eat it too. Sorry, you don't get it that way.