Well I'll be the contrarian here... I still own and shoot the 200-400mm f/4 VR. It is an underrated lens, amazingly flexible, and has very pleasing bokeh. The lens does not do well beyond 30 meters (90 feet) but within that range, it is outstanding. I use mine with a D500 and a Z6. With the D500 you get a 600mm F.O.V. which seems to be perfect for mammals. I also have a 500PF. The 500PF is the sharper of the two lenses and is hand-holdable. I can not shoot w/ the 200-400mm lens without a tripod.
If money were no object, I'd buy the 180-400mm lens, but the price to play is beyond my means.
regards,
bruce