They dont have to be beneficial because some people might have enough of those already and the problem lies elsewhere. For example if there is too much ROS then the only way might be to get enough antioxidants. Or if lipid biosynthesis is too slow because of some enzyme then more substrate doesnt help. But those two phospholipids you mention are key members of cell membranes so for some people it might work if the theory is correct. I view the theory as a long shot though because i view all theories of mecfs as a long shot at this point.