Just a heads up, I saw an article the other day talking about how new research might show that depression might not actually have deep links with chemical equilibria:
https://thenextweb.com/news/research-depression-not-caused-c...
It turned a mild bout of depression and long standing un-medicated adhd on it's head to the point that I feel like telling anyone who is looking for a "strategy" to first make sure their biology is in order. It helps loads. In any case, if someone knows how sound the science around MTHFR is I'd love to be wrong on the internet and hear about it (about 1 in 5 is the rate I was quoted for abnormalities with that methylation cycle).
Maybe what I was originally pushing back against was what I thought was the expression of certainty over specific chemicals causing depression, when I think there's a lot more we don't understand about the chemicals and even depression itself than we may admit, including any causal links.