Holding up marijuana legalization?

The U.S. cannabis industry is not a monolith.  Some players have reason to say that marijuana legalization is best left to the states

Here it is: Federal legalization of cannabis will hurt growers — producers. 

Today, foreign imports don’t come in, but once we legalize, existing trade treaties will automatically oblige us to allow imports. U.S. producers will say, “Ouch.”

Retailers and distributors and to some extent vertically integrated firms (like some) Multi-State Operators don’t join producers in this pain from legalization.

Are growers shrewd enough to be slowing down legalization? Or are the details just too hard for Congress to figure out anyway?