I guess all diseases were "created" then. I would actually call this describing an illness. Even ME would have gone through a similar process (as virtually every other described illness has).
To me, the difference is that in the case of other diseases, they are describing the specific symptoms that characterize that disease and differentiate it from other diseases.
But in the case of CFS as defined by Oxford and Fukuda, the only symptom that is required is medically unexplained chronic fatigue. Oxford doesn't require any other symptoms at all while Fukuda requires any combination of 4 of 8 symptoms, most of which are non specific. Both allow the inclusion of mental illness. Notably, there are 163 unique combinations of Fukuda symptoms but only 20% include PEM which is required in ME definitions.
IMO, basing the description of a clinical entity solely on "medically unexplained chronic fatigue" is not scientifically valid. Chronic fatigue is ubiquitous and ill-defined so that doesn't contribute to identifying patients. And there's no scientific rationale that I know of for grouping together all "medically unexplained" fatiguing conditions and studying and treating them as the same thing. It can't help but be a waste bin diagnosis that reinforces a psychogenic view of the disease.