Angry much? Some of what you say I agree with. Some I do not. The rest is of no value to me.
Chemical imbalances are often players in depression and other mental situations. This is particularly true of neurochemical imbalances ( too much or too little) of things like serotonin, dopamine and norepinephrine. I won’t bury you in references, but rather point you at Harvard; a pretty reliable resource. Search “what causes depression?”. Not to suggest that there are not other factors. Depression is highly complex with endogenous and exogenous forces at play.

One language point. Referring to an “endless plethora” seems somehow inappropriate. A “plethora” though an undefined quantity is a finite concept while “endless” is infinite. An infiniteness + a finiteness = zero.