If there is evidence for infection or abnormalities of the immune system for which there is validated treatment, that will be provided on the NHS, even if things ARE slow.
I can't speak to issues with the NHS specifically, but the experiences of patients with the NHS seem pretty much identical to issues I have with the Dutch health care system.
Basically we have GPs who know nothing about ME/CFS. They don't know anything about the relevant tests (mostly immunological) and are extremely uncomfortable being involved in directly prescribing treatments which they don't understand.
In a sane world, we would have ME/CFS specialists managing our treatment. But our national health care organizations don't have real ME/CFS specialists who can handle the treatment of infections or more general immune dysfunction. The specialist services in both the UK and the Netherlands are entirely centered around CBT, GET, and minimal symptom management.
So when we do find an ME specialist who is a real expert, who understands the testing and treatment of infections, etc, taking the test results and even prescription from that expert to the GP doesn't get us anywhere. The GP has no idea what the results mean, doesn't know who to refer us to, doesn't know if the test is reliable, doesn't know if the prescribed treatment is appropriate, and generally gets overwhelmed and frustrated by being forced to manage patients that the GP is not trained to deal with.
Some patients will get lucky and get a referral to an appropriate specialist in the health care system. But most of the time, that specialist will have preconceived notions about ME/CFS. This often results in minimal or no investigation, despite the prior test results - these specialists will completely disregard those tests because they are from a different country, or perhaps because they are outside their narrow area of expertise.
My own GP was sympathetic and even angry about some of the reactions from these specialists. But that didn't change anything, except that she'd run out of potentially useful people to refer me to. She still can't interpret my lab results, and has limited ability to order them redone in the national health care system, and she still can't responsibly prescribe treatments for them.
Hence I must disagree that abnormal results from reliable tests will result in validated treatments. Too many specialists have been the target of psychosomatic propaganda for far too long. They're still being told that testing ME patients will cause iatrogenic harm, presumably by reinforcing the "false" belief that we are ill. That's an insurmountable hurdle most of the time.