I think that the main concern here is bad scientific practices in psychology, rather than the personality of Sir Simon. He didn’t invent anything himself. The biopsychosocial paradigm was proposed by Engel in 1977. The precursors of cognitive behavioral therapy (CBT) had been around for a long time, but finally merged into CBT in the 1980s. The idea that ME was purely psychological was aggressively promoted in 1970 by McEvedy and Beard. They suggested that epidemic ME was mass hysteria, so Sir Simon’s initial proposal in 1988 that ME probably was triggered by an infection and perpetuated by psychological factors actually was a moderation.
Sir Simon just took ideas and concepts that were around and tried to adapt them to ME. He is good at networking and connecting with other scientists. He also understands that in an immature science like psychology, you have to sell your ideas rather than to prove them. You must make yourself heard and write many papers, not necessarily with any substance. I don’t think that Sir Simon is a good scientist with any deep understanding of the underlying theories. He motivated his model of ME with an irrelevant traffic analogy: in a hit-and-run accident, you don’t need to pursue the guilty party in order to start with the rehabilitation. However, even if you don’t need to know the trigger in ME, any serious scientist knows that you need to understand the nature of the injuries/symptoms to start with rehabilitation. The biopsychosocial theory for ME doesn’t deal with these details.
At some point, Sir Simon probably believed that CBT for ME was a good idea to try out. However, he is an ambitious career-oriented salesman for scientific ideas, not a scientist who follows up and checks if they really work out. That attitude prospers in an intellectual environment where theories are rationalized and never put to the test. He later got so invested in the model that there was no turning back, no matter what.
It may be provocative that Sir Simon has built his career on our misfortune, but as long as psychologists and psychiatrists nurture unsound scientific practices, pseudoscientific ideas like the biopsychosocial model for ME are going to thrive. CBT was tested for many other alleged psychosomatic illnesses, and it would eventually have been proposed for ME; if not by Sir Simon, then by Michael Sharpe, Trudie Chalder, Peter White, Esther Crawley, Per Fink, Vegard Bruun Wyller, Gijs Bleijenberg, Judith Prins, Rona Moss-Morris, or someone else. The key issue here is that psychology and psychiatry must change. Otherwise, they will gradually fade away and eventually become as irrelevant as astrology or alchemy.