The court was making the point that Congress has the power not only to regulate commerce, but also the instumentalities of commerce. The court stated:
"It is for Congress to supply the needed correction where the relation between intrastate and interstate rates presents the evil to be corrected, and this it may do completely, by reason of its control over the interstate carrier in all matters having such a close and substantial relation to interstate commerce that it is necessary or appropriate to exercise the control for the effective government of that commerce."
Congress may reach into the states to regulate an intrastate activity if that activity has a close and substantial relation to the regulated interstate commerce.
Again, 20 years before FDR.
"It is for Congress to supply the needed correction where the relation between intrastate and interstate rates presents the evil to be corrected, and this it may do completely, by reason of its control over the interstate carrier in all matters having such a close and substantial relation to interstate commerce that it is necessary or appropriate to exercise the control for the effective government of that commerce."
BS. Nowhere in this decision is there any reference to Congresses authority in such matters beyond the regulation of common carriers as "instruments of interstate commerce". You selected quote says as much:
by reason of its control over the interstate carrier