Chicken or the egg arguments get tedious pretty fast. It is the Supreme Court which gives the Congress the constitutional authority to act. The question of how to resolve such inteprative controversies remains for another day.
The authority for each/either to act is in the constitution. You were looking for the "final authority," and I am pointing out that Congress can reverse what it enacted, and thereby -IS- the final authority, as far as commerce clause encroachments go. That the Courts go along with it does not make Congress any less accountable for being the "final authority" on the subject.
-- The question of how to resolve such interpretive controversies remains for another day. --
I think the question has been asked and answered. As between the people and the government, EVERYTHING bottoms out on the perception of legitimacy and the willingness to use extreme violence.