Following your line of arguing (based on your characterization of the SC's logic), all activities can likely be shown to fall under the purview of federal law and federal law enforcement agencies as essentially all activities affect your local environment, and in turn all activities that interact with your local environment, which will include many activities directly or indirectly impacting commerce which will then impact interstate commerce.
This line of argument can be used to justify federal involvement in anything. This makes it useless in drawing any interesting distinction, nor does it address any of my original arguments.
I do think there is some truth to the argument that individuals' actions have global consequences.
However, I do not think the US Supreme Court has real claim to be the final, global arbiter. Usurping power is, however, the US Supreme Court's demonstrated prerogative. It's pretty much how the institution began its life.
This line of argument can be used to justify federal involvement in anything. This makes it useless in drawing any interesting distinction, nor does it address any of my original arguments.