Further, a lot of the other crime by cartels is funded by their marijuana business. It has been a cornerstone of their overall businesses the last 40 years.
That example of you gave, is fringe. The Knights Templar are not doing $25+ billion in annual revenue, which is what the implied extrapolation would be. The total annual 'revenue' for all Mexican cartels, is likely to be closer to $10 billion than not (RAND corporation estimated $6.6 billion for their drug trade, which is the majority of what they do).
There's a critical distinction between traditional corruption and illegal activities by gangs and similar, which is plentiful in 100+ of 195 nations, and the specific effects of the war on drugs. The war on drugs aspect of it, can be relatively easily neutered.
This is a well studied topic.
http://www.nytimes.com/2012/06/17/magazine/how-a-mexican-dru...
I doubt selling pot is more profitable than the rest of their activities combined. Take The Knights Templar as an example, they operated within a single state and made around a Billion USD in 2013 from Iron ore alone.
https://nypost.com/2014/03/17/mexican-drug-cartel-moves-from...