The PUFA argument is very complex, and there are no RDAs, or were not any RDAs when I looked into this. The big issue we have with PUFAs is the imbalance of omega 3 vs 6. The second issue is that we actually haven't had a huge amount of omega-6 historically ... we have had a huge amount of heat damaged omega-6, or trans fats. The third is many ME patients seem to have a PUFA deficiency, but it cannot be easily corrected with supplementation. Finally we need PUFAs for healing and fighting infection, so if you need either of those you need more. Omega-3 is probably a better bet for many of us, and direct supplementation can indeed lead to problems. However if someone is salicylate sensitive its very likely they will need more, at least some of the time. PUFAs are an example of a little more is often good, but a lot more is bad.
Vegetarians often have lots of omega-6, and some omega-3, all short chain. For anyone one with dysfunctional desaturase enzymes, and this might be common in ME, these are not rapidly converted to long chain PUFAs. This is not a good situation. Salicylate sensitivity usually occurs in this situation if there is a dietary deficiency.
Omega-3s can mostly substitute for omega-6s, and vice versa, but not entirely. Some essential eicosanoids only come from short chain omega-6s, or at least one, PGE1. A diet very high in PUFAs can also be undesirable, but the red blood cell deformability that is probably in ME might be improved with these fats. However any inflammatory tendencies will be worsened, even with omega-3s. (No, omega-3s are not antiinflammatory on balance, but they are much less inflammatory than omega-6s, and compete with omega-6s for enzyme binding and hence hormone synthesis.)
I trialed higher dose alpha linolenic acid for treating ME in the early 90s. It helped for a bit then stopped working.