I hear what you're saying about localised production, but then Megacorp has the benefit of economies of scale. Thus we see lots of things that can be done cheaply locally being done on massive scale in far-off lands and imported.
We can all brew our own beer easily for next to nothing, but almost none of us do. And the shops are full of imported stuff that undercuts much of the domestic craft stuff. My guess is the cannabis market would go the same way.
Yes, I know there's a home-brew subculture as well, but there are cultural differences between the two products. The vast majority of drinkers have already been weaned on mass-produced beer and tend to find the idiosyncratic taste of many homebrews less than palatable (and being one of the brainwashed masses, I speak for myself there). Whereas pot heads are already dedicated to a product that is grown in clandestine circumstances, as much by enthusiasts as hardened criminals.
Nobody knows for certain, but it's my guess that were pot prohibition lifted, a significant portion of the market would fall into the hands of home growers. Simply because it doesn't actually involve a change in behaviour for most people. Could be wrong about that, but it's just my sense of the situation.