I not agree.
Two part question. Part 1. Does Congress have the power to regulate (prohibit) the interstate commerce of marijuana? Not whether or not they should regulate marijuana. Simply, do they have the power to do so?
Yes, congress does have that power, BUT, they have passed and enforced laws that go VERY VERY VERY VERY VERY far beyond merely regulating the interstate commerce of dope.
As they do the ability to regulate interstate commerce of alcohol. Or tobacco. Or carrots. Which is why the 18th amendment was pretty useless, given how much alcohol is transferred interstate.