Symptom wise and quite a lot of the biology they definitely appear similar. The problem is the genetics studies show some overlap, about 80 combined SNPs for ME/CFS out of 270 and out of around 150 for Long Covid.

There is more to it than just different genetic mappings because while both conditions share mitochondria differences which compartments are different. Depending on how deep you dig into the biology they appear the same or quite different and a number of multiple point blood, urine and saliva tests can distinguish the diseases from each other.

I think at this point its more accurate to say they are overlapping conditions, they have similarities but they are different conditions. Sister diseases much in the same way there is overlap in Fibromylgia and Gulf War syndrome with ME/CFS and each other. Long Covid is another post infection Neurological and immune disease with unknown biomarker/core pathology. There are clearly a lot of measurable changes that are dysfunctional so its every bit as real biological disease as the others. What they definitely share is a high amount of debilitation, severe disability and patient reduction in quality of life on the same set of 280 symptoms in a very similar patter of prevalence.

Its also now a disease with very little research funding world wide as well so the situation is unlikely to improve for the 400m+ sufferers world wide.