Benzos are really nothing to write home about. The drugs all have clear indications that physical dependence comes in a relatively short time period --as in, with mere weeks of consistent use-- and that the primary factor for dependence is that withdrawal symptoms lead to exacerbated episodes of virtually all the symptoms (anxiety, insomnia, etc.) that cause people to be prescribed the drug in general.
This is absolutely true, which is why you have to be careful with them. That doesn't discount the actual benefits of using benzos, and I'm not a fan of when doctors prescribe them to be used daily unless it is for short term relief. There are still anxiety patients out there need a benzo once a week or so to deal with severe anxiety attacks, which wouldn't lead to dependence.
In the case of psychosis, though, your options are very much different. During acute psychosis you'll be on much worse drugs than benzos. When you are on the wrong anti-psychotics for your particular body chemistry, you will likely be in the emergency room and/or hospital not because you are a danger to yourself and/or others, but because your medications are causing you to pass out multiple times each day randomly and you hit your head, the drugs can cause dystonic reactions that cause you to lose control of certain muscles and they flex without you commanding them, they can trigger parkinson's symptoms (known as psuedoparkinsons or something like that), they can even cause your psychosis to be worse and trigger suicidal thoughts. That's not to say that anti-psychotics are the devil, they are kind of a necessary evil that you have to find the one that meshes with your body, but they are really awful drugs and all doctors know this. There isn't really an alternative to these drugs at the moment.
So when your illness is causing 100% of your day to be agitated causing lack of sleep, lack of perception, and constant onslaught of thoughts that do not belong to you and voices that do not belong to you, followed by trying to work through the difficulty of dealing with medication that you feel is trying to kill you (either delusionally as in "this is poison! the CIA is poisoning me!" or logically through just knowing that these medications are making you worse and trying to fight your way through the side-effects), being denied access to a relief to agitation because you can get addicted to it is silly. You're essentially fighting for your life at that point, either delusional thoughts that are telling you to kill yourself or you logically giving up entirely because you can't take the agitation anymore and killing yourself.
If long-term dependence issues would cause people to wish to not prescribe any drug, though, they wouldn't prescribe the anti-psychotics either because weaning off of anti-psychotics is incredibly dangerous and can also cause withdrawal that causes hospitalization and long-term use of them can cause permanent movement disorders (tardive diskensia).
I'm pretty sure that doctors in the U.S. vastly over-prescribe benzos simply because the recreational use and diversion are things that patients make people perfectly happy in the short term. If they become addicted, well, most of the time that becomes someone else's problem. In other words, because the drugs are legal and abundant, there's the ability to pass the buck infinitely.
I know there are probably some asshole doctors out there that might think this way, but I don't think this is the norm by a long shot. They do have to consider the risk of the patient getting addicted to it but there are many many cases of patients with serious conditions that need it. It's also kind of a judgment call when it comes to mental illness and issues of these kinds, so some might be better at knowing when a patient really needs it or not. Then there are the asshole patients who just want to be prescribed them so they can get high, which is also a problem they have to consider.
That will be the the problem with cannabis. The problems will never be physical addiction, withdrawal, etc. and yet there are easily spotted symptoms that at a wide enough scale will become an issue.
In cases of legalized cannabis we've had to date, cannabis has always been legalized in a very limited setting and the problem has never been so wide scale as to be a public health concern. But there are issues when retail cannabis becomes so easily available to so many. I don't think it's wrong, for example, to have real concerns about the degree to which people lose productive hours and impact their job prospects.
The same loss of productivity and health can still be had legally, though. Overeating, over-videogaming, over-television watching, over-drinking, over-fertilizing your lawn, over-gambling, over-whatever, are all things that can and do happen. If someone repeatedly doesn't do their job due to any of these things, we already have a solution to that. We fire them.