I don't think he is the father of the "all in the mind" view. He's certainly an important Perpetuator though, which amazingly he has done by proclaiming on many, many occasions that he doesn't believe it's "all in the mind".
Yes, that's true, Wessely did not invent the idea of psychogenic illness, but I read an article years ago which explained the history, and that Simon Wessely single handedly resurrected the notion of psychogenic illness from its then moribund state.
I can't find the article now (it may have been one of
Margaret Williams or Prof Malcolm Hoopers's articles), but it explained that the concept of psychogenic illness had died a natural death, I expect essentially because idea was untenable, due to lack of evidence.
However, Wessely in his early career revived it, and gave it fresh life, and this is the reason that not only ME/CFS was recast as psychogenic, but also other diseases such as interstitial cystitis, irritable bowel syndrome, fibromyalgia, chronic pelvic pain, etc.
Not to mention his application of psychogenic ideas to the Camelford water poisoning incident in 1988, and to Gulf War Illness, which is epidemiologically linked to organophosphate poisoning. His ideas were always very handy if ever you wanted to make a disease or poisoning incident disappear.
In this way, Wessely seemed to (perhaps inadvertently) become the medical equivalent of a mafia hitman: if you needed a disease or incident "disappeared" then you just needed to hire Wessely.
The disability insurance industry certainly found the services and ideas of Wessely and colleagues very useful in the 1980s, when there was a
5-fold or more increase in the incidence of ME/CFS (by these insurance companys' own claim statistics), and insurance companies such as UNUM could have become bankrupt had it not been for the "disease disappearance services" of Wessely and colleagues.
A Prof Malcolm Hooper article talks about this:
Magical Medicine: How to Make a Disease Disappear.