By definition, over simplification is not useful.
And reality seems to be so complex, that our experiential models of it must be a simplifications to some degree. So we must acknowledge that reality.
And there is a lot in Krishnamurti’s quote “It is no measure of health to be well adjusted to a profoundly sick society.”
Yes there are many chemical aspects to depression, including diet, as there are many social aspects, systemic aspects, cultural aspects, and aspects of individual choice.
Like most things in reality, it can be profoundly complex, and sometimes there are remarkably simple things people can do, and sometimes not. Every individual is profoundly unique, at the same time as we are all profoundly similar. Both are true.