I can't see much difference between the idea of a chemical inbalance and the idea of a biological problem, in the sense that both are pathologising something that isn't caused (directly) by a physical injury.
It was a fairly significant change IMHO, being pharmaceutical companies had derived PTSD to be a chemical imbalance between the left and right brain hemisphere, when in fact MEG dictated that PTSD is caused by a small part of the pre-frontal cortex. Obviously they can't open up brains and play around whilst the person is living, and they are pretty useless I guess when dead for such data.
My point is more... the original hypothethis was about adding drugs to rebalance an imbalance, when in fact quite the opposite is now proven, there is no balance or imbalance, nor a requirement for any drug interaction directly.
Agreed, a psychological problem caused a biological problem. Just a vast difference in the actual problem caused, its location and how it should be treated, and then what treatments are best for it.
Step back just five years, and PTSD was concentrated on the amydala and hippocampus, when neither are part of the issue with PTSD. Their functions are impaired as a result, though they're an effect, not part of the cause or the issue. Just the same as depression with PTSD has been shown not to be about serotonin synapses at all, like pharmaceutical companies dictate, and instead neurobiological imaging is showing it to be mood based, not biological based. Another "effect" and not an individual cause.
In other words, no longer are anti-depressants / SSRI's considered the first line treatment. Instead, behavioural change to lifestyle, limited and specific psycho therapy types and then if required, medication based at anxiety moderation only which corrects the mood simultaneously. Possibly anti-psychotics for severe cases to manage anxiety with manic episodes, all due to trauma.
I think it is all going to be quite interesting where things go as more science is a requisite to mental health, to demonstrate a validity within diagnoses. Maybe science may force many of them out of the book as nothing more than social inadequacies versus mental health conditions.