Regarding cortisol levels: there are three stages of adrenal fatigue. In the first stage cortisol levels are high. In the third stage cortisol levels are low. Lowering cortisol by various methods (meditation or supps) would only apply to stage 1 adrenal fatigue.
Many ME/CFS symptoms can be attributed to Stage 3 adrenal fatigue. Stage 3 is self perpetuating and very hard to get out of.
I think the goal would be to have normal cortisol levels, not too high or too low. For this you have to treat adrenal fatigue.
The reason for the adrenal fatigue in the first place is due to a partial methylation block. If you're not methylating, then you can't produce adrenal hormones. This is also self perpetuating, unless you treat it by taking active folic acid and B12.
The reason for the partial methylation block is a chronic stressor. This can be anything from abuse to viruses. It just has to be chronic to start the process and tip a person into a self perpetuating cycle.
That being said, millions of people are under all kinds of chronic stress, yet they don't get ME/CFS. I believe there has to be something extra going on like XMRV to explain why we get ME/CFS while others under the same stressors don't.
So there are three legs to the problem:
chronic stressor, leading to methylation block, leading to stage 3 adrenal fatigue
I think some people have been lucky and gotten better treating 1 or 2 of the legs, but many people will ultimately need to treat all 3 of the legs to get completely well.
There is an additional complication that happens with adrenal fatigue, which is the development of food allergies. They become chronic stressors themselves, which perpetuates the adrenal fatigue. This would explain why some people have changed their diet (ie eliminated their food allergies either by choice or accident) and gotten benefit.
So you would have to simultaneously treat 1) chronic stressors - XMRV, Lyme, other infections, food allergies; 2) also the methylation block; 3) also adrenal fatigue.
But given that we may not have access to the more heavy hitting and expensive treatments (ARV's, AV's), working on any of the others that you can (food allergies, methylation, adrenals) would make sense to me.