I'm always open to differing views, so would be interested in any recent papers pointing to a psychosomatic cause, especially as this seems to be an area active research is moving away from.
I completely agree the mind/body need to be treated more as a single entity, but the researchers and clinicians I've been engaged with are most certainly looking at this in a non Cartesian way. Nb these are not general practice doctors.
Again, I'm comp sci rather than medical, so my experiences are anecdotal but a good many of the CFS patients I've known have not been under chronic stress with the often exception of CFS seemingly being triggered by a viral infection such as glandular fever. I can't comment on whether cortisol levels remain high.
Fundamentally there is so much we don't understand about what may in fact be a group of illnesses, hence why people's personal stories seem to fall into two or three conflicting camps.
We need more data to go on, which is why I've a side project looking to address this which will hopefully lead to more areas of research.