The problem is that these "studies" have is they make no differentiation between how that Cannabis is consumed. You get the impression that they just act like everyone just smokes joints. Even when i was smoking i almost exclusively tried to smoke through water with a small bong. With DH vaporization there is even less irritation of lungs throat etc. Also what about edibles in the consumption mix?
So unless they even address these points i think there is a critical lack of science going on. Even for researchers they want to make a big SPLASH headline so they will get their next staunch of funding.. And political groups will try and use this for their own purposes.
Yes, there are so many variables that are not systematically addressed in these studies, such as frequency of use, amounts used, methods of ingestion, potential pesticide exposures, etc., etc., etc. Also, there are a host of issues associated with self-report data.
At best, the current meta-analytic study suggests that it is possible to use cannabis in ways that appear to be unhealthy. IMO, until better controlled, more granular studies become available, we are still essentially in the dark.