The black market is destined to collapse. It only exists now because legalization happens only in certain areas, which means that leads to potential for trafficking and feeding the black market, but when sweeping legalization comes about, the profit margins drop. Even for licensed/legal grows, much less black market. I've heard people say this before; "There will always be a black market"...I disagree. Maybe there will be people that will sell a little here and there that they grow, but generally, there won't be much benefit. Like people who make beer or wine in their basement. They aren't swimming in cash over it for the most part, but it's a hobby in which they make a little cash. Compare that to alcohol during prohibition and you will see that an underground market for alcohol doesn't really exist and neither will a cannabis market in that realm.
As to other claims of better flower, it's hard to define "better". I have seen some people apply some insane pesticides on their flowering plants. Search this forum and you will see examples of it. I know growers who have unapologetically sprayed their crop with dangerous pesticides and, in talking with them, they knew how dangerous it was, but they simply didn't care. This blows my mind. Screw that...I had someone contact me today about our state regulations because they had a guy come visit their facility from out of state and they were hoping to find a loop hole on how to apply pesticides outside of the window (in other words, to spray fungicides on flowers which is against our regulations). And these are people WITHIN the boundaries of regulation, still trying to find ways to apply pesticides when they shouldn't.