I completely understand your frustration with the lack of knowledge and research in ME/CFS. It's a scandal, given the prevalence and seriousness of the condition. Unfortunately, after Covid, ME/CFS was even more politicized as part of the long-Covid discussions and got caught up in the culture wars. I have several friends with ME/CFS and they basically say the same things you do - ignorant doctors, high cost due to medication usually being off-label and not covered by insurance, and even friends don't take the condition seriously.
ME/CFS research is severely underfunded. The reasons for this are not simple, it's partly due to the complexity of the disease which, as cynical as it is, does not make it an attractive research topic for ambitious scientists. Same goes for "Big Pharma". Clinical trials for ME/CFS are extremely complicated, and hence expensive, due to the myriad of symptoms in how the condition can appear. It makes research in this area very difficult and expensive. There's very little funding for ME/CFS research, and that needs to change. Unfortunately, especially in the US, this is not going to happen for Kennedy reasons.
The Bayesian statistics thing is a bit of red herring, though. While your are correct that the math is old, the needed compute resources for doing Bayesian modeling on large trials was simply not there until recently. But it is also correct that it also took a long time until there were official rules regarding this from FDA and EMA. These regulatory things move very, very slowly.
Unless you’ve had ME/CFS you cannot understand how bad it is, I’ve had it and I still have a hard time comprehending how bad it was, I am occasionally reminded and it’s easy to forget. While it won’t kill you it’ll destroy your life until you’re ready to kill yourself.
The UK led the world with explicit psychologizing of it in large part to prevent insurance companies being liable for such an expensive and debilitating condition. A legacy that continues to this day, the main people responsible are still very influential. Fauci was instrumental in diverting research away from the autoimmune aspect and preventing a lot of important research. The $1B set aside for LongCovid appears to largely have been wasted. The official classification for hEDS was explicitly changed to reduce the number found so that it could remain a rare disease and continue to have access to specific funding for rare diseases (goal seeking). I could go on and on. It is a highly dysfunctional industry with many perverse incentives pulling it in all sorts of directions. There was the healthy at any size movement despite obesity being a massive cause for mortality, perhaps the only stronger signal would be smoking and consider how long it took them to figure out smoking.
There have been insanely impressive improvements to medical science but this seems to be largely due to tooling and access to information rather than the lumbering bureaucracy which appears to do very little of benefit.