I think you're right that the research isn't up to par. But I also think there's a lot of empirical evidence to show that there are some use cases. I don't expect any scientist, chemist or doctor to recommend that I burn plant material and inhale the combustion products. But what about a hospice, end of life situation, to improve quality of life?

You mention psychotic disorders and concentration. I have PTSD and normally cannot concentrate on anything for more than a few minutes. The best my psych can do is something that makes the episodes less intense, but they still happen. I normally cannot sleep unless I am so exhausted from being awake for typically 30+ hours, and then I'm usually awoken by a terrible dream within a few hours. Guess how I cope? I smoke and my tolerance is such that I don't get high anymore, but I still receive other effects that are beneficial. I can concentrate and give attention to myself, my family, and my work. I can go to sleep and wake up at a normal time. Therefore, I think there's some demonstration here that mj can be therapeutic or helpful in at least some cases.

Fun fact: the medication I'm prescribed is new and was discovered empirically and its mechanism of action is unknown. I know I am risking cancer and two lungs full of thick tar by smoking. But for the medication, all they have is "we haven't seen it hurt anyone yet." I think maybe the community knows more about pot than this one.

Edit: Before I started smoking I was on Xanax, which I think carries a greater risk from daily use than smoking.