IMO, the whole purpose and meaning of the CMRC rests on the success of the large study; and everything else about the CMRC can be considered froth in comparison.
If the big study is a proper solid study then the CRMC will have been massively worthwhile. I like the idea of the large study. And in principle the issue of a broad cohort isn't too problematic because participants can be sub-categorised by various diagnostic criteria (CDC, NICE, IOM, CCC, ICC).
If the study uses the UK's biobank, then I won't have any problems with the patient cohort. If I remember correctly, the biobank patients are diagnosed using CDC and CCC. The biobank patients would be a heterogeneous group, but if the researchers recognise this and are aiming to distinguish subsets (which they are) then this isn't a problem.
But... I agree with what people have said about the major issue of bias on the collaborative board. And if Esther Crawley and colleagues are in charge of recruiting (e.g. recruiting from their clinics) for the study, then we potentially have a major problem, whatever the official recruitment criteria. It has been said that Crawley retracts a CFS diagnosis if her patients don't improve after 'treatment'. In which case, long-term patients are 'disappeared' from the stats. And, although we will never know the exact details, the PACE trial excluded patients with neurological symptoms, and there would be similar potential opportunity to exclude severely affected patients with neurological symptoms from this big study for similar reasons. Such a scenario would obviously introduce serious bias into the study, no matter what the recruitment criteria are. So they need to be removed from the recruitment process to gain the confidence of the patient community. (Crawley and her colleagues don't recognise ME/CFS anyway, because they don't understand the illness: they are only interested in false illness beliefs.)
If the study doesn't have the confidence of the patient community, then we know what happens. The patients' concerns are ultimately validated, and the aftermath is a long-drawn-out-process, divisive, and painful for all sides.