It might be interesting to debate the evidence for this but I suspect it may not be quite as it seems.
I have spent much of the last ten years studying the approach of the philosopher scientists of the seventeenth century to mind and body. What has become clear to me is that the present day distinction between mind and matter is actually very new and largely based on dumbed down schoolroom teaching that does not actually reflect fundamental science. What is new is the idea that there is some stuff called matter, based on 'mass' that may or may not be different from 'mind' or 'spirit'.
Three hundred years ago 'mind', 'life' and 'movement' were much more synonymous. Anything that moved was alive and had mind or spirit. That might seem more a popular view than the view of refined science. However, the scientists of the Renaissance/Enlightenment were educated in Greek ideas (and often Indian and Chinese ideas) and they were well aware that the intuitive idea of matter contained a paradox. Macroscopic matter cannot be explained by microscopic or infinitesimal matter. You hit a contradiction. So people like Galileo, Descartes, Hobbes, Hooke, Leibniz, Newton, were all aware that 'matter' was more or less an illusion. Deep down everything must be 'spirit' in some sense.
Descartes tried to identify a dichotomy in the way things work. In fact he identified a crucial dichotomy that persists in quantum physics. But in a sense Descartes great contribution was to show people how productive it could be to be specific enough to get things a bit wrong. Within 30 years of his death they had got it right.
The present day concept of mind versus matter has a lot to do with a very short period around 1900-1925 when scientists seriously suggested that matter might be made of little billiard balls, or solar systems of billiard balls, despite the objections of the Greeks, who had largely been forgotten about. Then in 1927 billiard balls were completely abolished and everything was spirit again - Planck's units of action. But nobody told the schoolteachers.
This may all seem a bit distant from our ME concerns but I think two things may emerge.
Firstly, I suspect that the 'psychosomatisation' of illnesses stems mostly from the nineteenth century. The present day mind body split I think emerges as the 'natural philosophy' of Newtonian science forces a 'two culture' separation from religion-driven 'philosophy' (as we now understand philosophy) maybe focused in Germany following Kant and Hegel. Out of this emerge Freud, Charcot, etc. It is interesting that the East London MUS service employs German psychosomatic physicians even now.
This is a gross oversimplification but it might be interesting to explore a bit more (probably on another thread).
Secondly, there is the knotty problem of how you shift the popular culture, including the popular medical culture, towards a more useful analysis of mind and body that would show the psychosomatic view to be hot air. The problem with this is that I am pretty sure that a realistic understanding of mind and body involves moving to ideas that are so seriously counterintuitive that there is no hope of more than a tiny minority of people understanding them. They fly in the face of genetically programmed concepts of selves and persons. A counterargument to that is that they are not so distant from the ideas of the ancient Indian Vedas, which became standard teaching. But although Leibniz translated these ideas into a Western analysis and essentially gave us the complete solution almost nobody has understood Leibniz's writings.
I think we may be back to the idea that to turn around the psychosomatic account of ME we need to be able to show its mechanism. We need the biomarkers and the pathophysiology. Whether that will leave MUS untouched in terms of IBS and so on I don;t know, but ME is a bit of a poster boy for MUS and if it turns out to be MES (medically explained symptoms) then maybe the whole house of cards really will fall.
