MCAS is not ME/CFS, nor even a common symptom of it. And I do agree that supplements can be helpful for certain symptoms, but they certainly do not cause recovery or near-recovery of ME/CFS.
Full-blown MCAS is uncommon in ME/CFS but less severe issues with food intolerances, histamine, prostaglandins etc. are common. Severe MCAS is actually in some ways worse than ME/CFS because every time you eat you are in danger of anaphylaxis. You also end up in a situation where you cannot take any medications including antibiotics so something like an ear ache can last for months because you can't treat it. Also, it can lead to serious complications such as gastroparesis and needing to have a feeding tube put in. Not saying that ME can't lead to death but the threat of dying is much more immediate with MCAS.
Dietary changes and supplements have an enormous impact on my MCAS - both good and bad - even though it's a serious and complex disease. Most people on this forum have experienced negative reactions to foods and supplements, sometimes profound and prolonged negative reactions. If you are willing to grant that some foods and supplements can make an ME/CFS patients feel worse, even a lot worse, I don't see why the reverse couldn't be true also.