I can't speak to exactly who uses this terminology, and I have not heard it from a medical professional, but I feel like it lingers on, like in medication pamphlets.

Because fundamentally, I think, it is necessary to try to get people to comply with medication that seems to help sometimes, while avoiding the reality that the way it works is not known.

No, I agree with you. I do not find psychiatrists believe that mood disorders are only chemical imbalances in the brain.

I have come across people have been led to believe it’s a chemical imbalance by psychiatrists, even in the last few years.

It may not be the modern psychiatric view, but it’s also true that psychiatrists are just doctors, and many of them are very slow to change from what they were taught in medical school.

it's a default API for brains, but ideas will trigger neurochemistry too .. well I'm sure you got that already