Buying into idea of chemical imbalance causes psychotropic medication discontinuation problems

As mentioned in my previous post, I have been reading The sedated society: The causes and harms of our psychiatric drug epidemic edited by James Davies (2017). The chapter by Luke Montagu, entitled "Desperate for a fix: My story of pharmacetical misadventure", describes the problems he had discontinuing psychotropic medication after "having bought into the idea of a chemical imbalance" when he was taking medication. Luke's father is the Earl of Sandwich, and one of the co-chairs of the All Party Parliamentary Group for Prescribed Drug Dependence (see previous post). As Luke says:-

[P]sychiatry, in league with the pharmaceutical industry, chooses to perpetuate two fundamental hoaxes. The first ... is that the suffering we call mental illness has a biological basis, like cancer or diabetes, caused by an imbalance of chemicals in the brain ... The second hoax follows on from the first, namely, that today’s drug treatments target and correct this chemical imbalance, just like antibiotics fight infection or insulin treats diabetes.

He goes on:-

One day these beliefs and treatments will seem as misguided as the theory of the four humours, when bloodletting, blistering and purging were believed to restore the correct balance of blood, phlegm and bile

As I said in my previous post, historically it helps to see the chemical imbalance theory as a myth, as it's wrong like humoral theory. I hope Luke's right that it will be found to be misguided, but there are powerful reasons why people do believe it (see eg. previous post). Maybe one of the major reasons for getting rid of it is to prevent people developing discontinuation problems.