Yes, it's complex, perhaps even to the point of being largely beyond our understanding, but unfortunately there are countless practitioners offering these niche one size fits and explains all diagnoses. Preconceptions and confirmation biases are rampant, in my personal experience and that on behalf of my son.
I recall one "LLD" who not surprisingly immediately decided I had chronic Lyme even though I don't have any of the "hallmark" symptoms. Test comes back negative, he says he doesn't believe it do this other more expensive one. That test comes back negative. He says he doesn't believe it, do this new and even more expensive one. At that point I said you know what dude, I am pretty damn sure I don't have Lyme, and moved on.
I completely understand your frustration. Whatever an LLD is, I'm well familiar with even MDs who have their hobby-horses and see everything through that. Dr Klinghardt (not even sure if he's an MD or a ND) sees Pyrrole Disorder/Pyroluria (PD) through his Lyme glasses, Dr Lam (MD) sees it through his Adrenal Fatigue glasses, for others it's iron dysregulation, mercury, pretty much the slew you mentioned.
The Walsh Research Institute are pretty much the authorities on PD and the other related syndromes now, Walsh worked with Pfeiffer who worked with Hoffer and he inherited all the clinical data as well as continuing the clinical research work. This is why they (and Dr Walsh specifically) might seem to have a cult following, being the lone giants in the field. They get their funding as a charity, proceeds from
Dr Walsh's books, and by training MDs in the protocols. They figure only MDs have the Biochem needed to apply the theory correctly. I'm lucky in Australia we have the highest number per capita of these
wonderfully competent people otherwise I might have had your own problems.
I know you're wary of one-size fits-all, but my observations have led me to conclude that these modern "genetic" diseases are really triggered by what Walsh causes
"environmental insults" which cause changes to the DNA or the epigenetic switches through oxidative stress (OS). These could be by pathogens, stress, or toxins, all of which play their part and may act in a cumulative or synergetic manner. Diet, lifestyle, and contaminants play a big part in this I see from my new perspective and is another reason I'm an antioxidant fiend now as a prophylactic.
I have a very dear friend who was struck down with ME/CFS due to a combination of all these it seems. Of concern especially is the repeated bouts of EBV she had which apparently has the ability to cause changes to mitochondria genes, as well as these genes being especially vulnerable to metabolic/toxin OS.
Mitochondria dysfunction looms ever larger in my mind as a factor in CFS/ME, ATP being fundamental to body processes including nutrient metabolism. It would explain the surge/crash cycle, as ATP builds up during resting periods and gets depleted leading to the dreaded crash.
Anyhoo, I have things to do. I hope things work out for you.
Dom