Says you. You offer no sources but yet personally attack him. His take on the situation is every bit as valid as you feel yours is. Maybe he consulted "experts" too.
While I wouldn't at all be surprised to hear that pot accounts for a large (estimated) proportion of the Mexican cartels' income, I too would be interested in knowing from where these 60/40 figures are coming.
Also, even if pot were legalized, I have a feeling that trafficking in it would still occur. It'd likely be reduced, sure, but stolen and/or trafficked goods are always going to offer bigger profits than those transported via legal means.
Beyond that, should marijuana profits be reduced, I'm quite certain that without proper law enforcement in place to dissuade them, the cartels would simply move on to something else, or would increase their efforts in existing areas. Likely one of the reasons they earn so much (purported) money from pot is that I'd imagine the overhead is low, the expertise required to produce it is minimal, and the facilities are already in place. Without marijuana, who knows, maybe they'd drastically beef up their meth and prescription drug production and sales. It's not like the Italian mafia suddenly disappeared once prohibition ended.