Everything from chronic theft to murder to and many things in-between could all be viewed as medical disorders in many cases. That isn't particularly relevant to whether or not it should involve jail sentences. Cannabis is not an addictive substance more than many other crimes.

Pointing out cannabis isn't harmful is what I'd expect a surgeon general to say (and I think they should say), but he didn't. Instead, he made a "value" argument which is strictly non-medical.