If I understand what you're saying, you think that some subset of people with chronic fatigue syndrome and fibromyalgia have undiagnosed thyroid problems that do not show up on standard tests, therefore treating them with dessicated thyroid could help.

I think that is plausible, and more reasonable than something like "all CFS and fibromyalgia can be explained by endocrine problems". It also seems to match the experience of some doctors who treat a lot of patients with these conditions.

There is also a difference between "helps to some extent" and "is enough to completely cure".

I would add to that:

The manufacturer of dessicated thyroid in the United States a few years ago added different fillers to the pills that can interfere with the medication. So if you are thinking of experimenting with that, check up on the non-active ingredients used, and precisely who manufactures it. There are differences between the pills from different manufacturers, they are not all the same, even if it looks like they ought to be interchangeable at first glance.

There are a number of doctors treating people with bioidentical hormones, that is, hormones in the same format that the body uses, not synthetic hormones that have similar, but not identical, structures. Bioidentical hormone supplementation seems to help some people. If you want to read up on that, Dr. Alvin Pettle has some lectures and books available where he goes into why, for example, horse hormones, derived from horse's urine, are problematic when in human women's bodies. In the context of thyroid problems, an alternative to dessicated thyroid would be bioidentical T3 and T4.