A lack of understanding why these drugs work does not mean that the diseases they are often successfully treating is "phony".
But there are two problems with the current consensus that I take issue with.
One is the that it's easy to medicalize normal human variation. Two years ago after an intense battle, I lost my mom to brain cancer. That same year, I lost three other people and had some other majorly bad things happen. At some point I talked to a therapist about depression. She agreed I matched the symptoms, but disagreed that I was depressed. I was grieving, and in her view I should work through it, no matter what other people thought.
I retrospect I can see she was right; I had work to do. But at the time, it would have been very tempting to take a pill that suppressed the symptoms. That's certainly what some people who told me I should be "over it by now" thought I should do. Our current society just doesn't have a lot of room for that.
The other problem I have is that we are putting things like depression all on the individual and some posited internal flaw. I think that's a lazy and disrespectful conclusion given the state of the art. For example, we are discovering that nighttime artificial light triggers depression in animal studies, and we know simulated extra daylight during the day can treat it in humans. For those people, their depression isn't a disease, it's an unintended consequence of our artificial environment. Daily pills to shift brain chemistry are one solution to the problem, but they aren't the only solution.
I think the disease model of medicine has been incredibly successful in improving human lives. But it has limits, and I think mental health is one area where we are overfitting the data to our model.
Would that were true! In fact the science is not very strong at all. We have descriptive sets of symptoms and we have classes of drugs discovered serendipitously that seem to help some sufferers, but despite 30+ years of effort we have little more than post hoc justifications for mechanisms of action and underlying causes.
The chemical imbalance theory has very little evidence going for it besides circular reasoning.
We are at the point in the science of mental illness where we go and categorize things -- this animal has a spine, gives birth to live young, and is warm blooded -- okay put it in this order. We need a Darwin, or at least a Mendel.