“Common Phenotypes Hypothesis: that recognisable neurological presentations may arise from different underlying mechanisms, and that identifying a symptom pattern does not necessarily establish its cause”

I guess you do not realise that this is already an established part of medicine and not a new hypothesis you’ve developed. Movement disorder symptoms such as tremors, myoclonus, chorea, ataxia, etc. can have numerous underlying mechanisms and causes. The phenomenology can help with the differential diagnosis. For a tremor, neurologists will define the clinical presentation (amplitude, frequency, direction, history, testing, associated signs, etc) and then what causes it (acquired, genetic, functional, etc). Tremor classification explicitly separates the clinical syndrome from its etiology. The exact mechanisms underlying motor symptoms are not fully understood across most conditions. A functional tremor and essential tremor both have proposed mechanisms and they will present differently on exam. If this is all because you are concerned for patients, rather than having some sort of vengeance against FND), you’d also be concerned about all other conditions that are clinically diagnosed. Your proposed hypothesis does not seem to introduce anything new to what is already standard medicine.

It’s important to note that disagreement amongst clinicians is not unique to FND. It is widespread throughout medicine. Rheumatoid arthritis is misdiagnosed in about 1 in 5 patients. This post doesn’t add anything useful as it just confirms FND doesn’t differ from the rest of medicine. You’re using it to plant seeds of doubt amongst readers though.