Depression is NOT a synonym for "bad mood" or "being tired", it's much more serious than that.
Totally agree depression is a serious mental illness, but this description is like describing bugs as a "debugging deficiency". We know depression and bugs can be fixed with debugging/ssris but just because we can fix them with it doesn't mean the opposite is the cause.
For instance in addition to serotonin and nor-epinephrine we also know glutamate (nmda and ampa) is involved, as well as opiates, gaba, bdnf, dopamine, and inflammation.
The chemical imbalance explanation is a very simple and convenient one. It pairs nicely with the don't like the situation, apply a patch (pharmaceutical or not), repeat. The patch mutes the signal and the theory is that since the system is functional everything is fine except we haven't dealt with the underlying emotional issue. It makes sense to me given this situation why some patients have trouble staying on medications. We can list as many substances as we want, but to me these solutions pair best with lifestyle changes which are more hard to implement/navigate which most likely why we default to patches when maybe what we need is a full version update.