I'm not going into this debate with you any longer...
I've posted my work from the lens on FM as well. I am highly doubtful that the 200-500 could produce a better image. Having owned three, I know what the lens can produce. However, I recognize that you are extremely happy with your lens. I suggest that you keep it, use it, and protect it.
I have been photographing nature and wildlife since I was a researcher in the Pribilof Islands, AK in 1986. I have shot everything from Nikon, Contax, Leica, Hasselblad, Toyo, Mamyia, Canon, and Pentax. I have owned and used countless varieties and brands 300mm f2.8 ED (AF, VR, IS, AiS), and Nikon 400mm f3.5 EdIF, 600mm f4 AFSII, 500PF, 200-400VR, 200-500, 300 f4 D,AFS,PF, 400 f4.5S, and 800PF. I publish my work, I do fine art galleries, I write articles for magazines, and I teach photography. I pretty much know what a sharp photo looks like... if not, I should just ditch the gear and learn how to fish.
This image was shot with a Z8 in FX and is about 37MP downsized for BCG and FM.
I have seen a lot of work with the 200-500 from others as well as myself... the lens is good but it is no better than the 180-600. Furthermore, as I have said many times... there is more to a photograph than how sharp it is. If you would like, I would be happy to pose crop of the face so you can see the feather detail... but as I keep saying, there is more to a photograph than how sharp the image is.
good shooting,
bruce