The question about blinding is a real problem, but I'm going to let others reply to that part.
Questions about objective measures are another matter. Even without the kind of convenient biomarkers researchers would like we can easily show that physical performance of ME/CFS patients is far below any reasonable standard of health. The PACE researchers compared data with data from a study of the general population which was not limited by age, and did not exclude patients with serious diseases like heart failure, even though their cohort of subjects did exclude extremes of age and quite a number of physical illnesses. They further pretended that those performance measures from the general population were normally distributed when this was manifestly not true. This then resulted in claiming the patients in the study were only one standard deviation below the mean in performance, which wouldn't sound very serious to anyone thinking in terms of normal distributions. Results on a "walk test" grouping these patients together with those having stage II heart failure should change opinions. It undermines the argument for this approach that the same authors then altered the threshold for entry by 5 points, saying that this difference did not invalidate the study. If a change of 5 points for entry was insignificant, so would a change of 5 points for recovery be insignificant evidence of any therapeutic success.
Recent work by the CDC also shows ME/CFS patients they have chosen also have a very low standard of physical performance. What two small studies by
Van Ness and
Keller showed was that some patients exist who suffer a decrease in exercise capacity lasting more than 24 hours following exercise. This undermines the rationale for prescribing exercise for them, since they would not be able to engage in daily exercise without losing ground. We are now seeing that government researchers can define the disease and choose the patients to test in such a way that the prolonged decrease in function is not apparent, though the ability of even the patients they chose to
benefit from exercise remains in doubt.
What gets lost in this dispute is that people having the characteristic drop in function during the time they report symptoms of PEM really do exist, and prescribing exercise for them within such a period should be contraindicated. I'm am willing to stipulate that 98% of the population does not show such a drop. If this were not so, experts in sports medicine would not have been shocked to discover exceptions at this late date.
A completely separate study of patients reporting exercise intolerance with dyspnea showed that a significant percentage had low cardiac fill pressure, a very solid objective measurement. N.B. these patients did not have either pulmonary hypertension or classic heart failure.
Aside from questions about diagnostic criteria and cohort selection we have another question to deal with: how do you separate the patients who will suffer permanent damage from a therapy from those who will benefit? There is no reason to believe the fabled diagnostic eyeball could separate the patients seen by Systrom's group from those with less severe problems. Nor were most doctors who participated in the two other studies easily able to distinguish patients whose capacity for exercise would fall.
Official positions on this matter amount to claiming such patients do not exist because 98% of people are not like that. It might also be that governments do not care if a recommendation that benefits most other people causes long-term decline or even death in a few exceptions.
Added: Concerning the "few exceptions" above, you might compute 1 or 2% of your national population to estimate how many people could be harmed if exceptions are ignored. ("So official spokesperson are you trying to imply that you would be happy if several million Americans did not exist? Are these steps you are taking intended to make that true?")
Just as an old anecdote I will mention going to a young doctor for a previously scheduled check-up when I had a viral infection with "flu-like symptoms". I asked if this meant I should relax my regular exercise routine. (This was before I reached my current state of disability.) He suggested that it would do no harm to "push through". An experienced cardiologist said "absolutely not", since it would be impossible to tell "flu-like symptoms" from a more serious condition like viral myocarditis before doing permanent damage to the heart.
The problem is not that the advice would not benefit many other people, it is that the exceptions have major downsides.