A person born in the US to citizen parents would be a citizen without INA 301(a).
Then why wouldn't such a person be included under section (a): a person born in the United States, and subject to the jurisdiction thereof?
So INA 301(a)/8 USC § 1401(a) are simply declaratory, but (g) is an affirmative act? What about (b) through (f)--which ones are declaratory and which ones affirmative? On what basis do you make the distinction, other than your preferred outcome?