treating addiction as a disease has brought us drugs like chantix (varenicline), among others. it is very profitable for them to first create an addiction, then offer the solution.
i agree that the drug companies will continue to profit from pitching addiction as a medical problem, and it is very true that preventing addiction is far easier than treating it.
regrettably, preventing addiction is not something our society is geared up for. if anything, we are in the mode of causing addictions for the purpose of profit -- whether by social media or by opiates. our society inflicts enormous pains on people and drives them to escapism via drugs as a result. the rat park experiment is very enlightening in this regard: https://en.wikipedia.org/wiki/Rat_Park
the treatments for depression are, unfortunately, a way of compensating for the deprived and stressful environment in which we live. it is this environment that i suspect is the root cause of the widespread prevalence of depression, though there is probably a sizable population of people who develop depression regardless of their environment. antidepressants are intended to help the latter group, but are used for both the former and the latter.
as we know, the antidepressants don't definitively solve any underlying neurobiological problem, though they may save a few lives and empower some people to change their life's circumstances and ultimately recover. is it better for someone to be reducing their pain using antidepressants rather than street drugs? certainly.
you mention ADHD, but i think your angle on it isn't exactly in the same bucket as depression. people with ADHD are at extremely high risk of addiction. i imagine that if we could reliably treat ADHD and increase awareness regarding the disorder's attendant comorbidities, we would be preventing many addictions before they could develop.