Yeah I guess so, you're not going far enough down the cause and effect chain, you don't seem to be asking yourself what is causing the chemical imbalance? The thing is, every single thought is accomponied by a change in the chemical mixture in the brain. So you could explain the cause of every single thing happening in the brain as a chemical imbalance, which is correct, but doesn't explain anything at all really, it's just giving it a different name.