If there was neurochemistry that was uniquely and consistently associated with depression it still would not follow that "direct physical intervention" is the best treatment approach. Lifestyle modifications and behavioral interventions also change the brain. It is standard to combine both approaches.

No one really disagrees that depression has physical causes. What other causes are there? I am guessing you are not a Cartesian dualist.

>Really turn-it-off-and-turn-it-back-on-again thinking.

Unfortunate analogy since the article you linked talks about "resetting" the brain with psilocybin.