Yes, I think the major problems of selection bias, even with such a large sample, make conclusions about sex differences, and also subsets based on onset type unlikely to hold.
There's a typo there, a missing 'are'.
I was disappointed to see this. There are many people I would have liked to see acknowledged before Holgate.
Clearly there are different views about Holgate's contribution to ME/CFS research. I think even his supporters would have to agree that it has been, at the very best, mixed. If he was not actually part of the BPS establishment, he certainly seemed to allow it to have considerable influence over the CMRC for far too long. For example, in 2017 he said that Crawley had the full confidence of the CMRC executive board. He described FITNET as 'quality research'.
He seemed willing to allow senior BPS players to take major roles in MEGA, the version of DecodeME that would have gone ahead if people with ME/CFS had not objected. In many of his communications he seemed patronising about people with ME/CFS, for example suggesting that it was our inability to understand what MEGA was trying to do that was the reason for the considerable opposition to that project.
I'm a long way from the UK politics of ME/CFS, and perhaps Holgate was playing a long game and did make a difference. Perhaps other sorts of politics are at play in singling him out for thanks in this paper. I don't know. But I was disappointed to see his name there.