It's a bit of hypothetical discussion, isn't it? Who on mother earth will use the D850 at lower than maximum resolution?
It's like driving on the autobahn in a Porsche and to decide that 50km/h is good enough today.
I think many sports/wildlife shooters may well choose crop for the reach and smaller file sizes, a four second burst at 9 Fps on FF will produce quite a stock.....and when you get back to the computer you might pick one or two shots!
I still see it as a do it all camera!.....