I’ve been living just outside Yellowstone in the town of Gardiner for over a year now and I’m in the park shooting at least 4 days per week and 6 days per week in the most active times of the year. Although not listed, I use the Nikkor Z 800 mm f/6.3 VR S lens with a 1.4 TC almost permanently attached, not just because of the long distances but to bring closer targets closer. There are days and circumstances where atmospherics make that lens unusable but that would also be true for the 600 and usually the 400mm lenses. I carry on a body strap the Nikkor Z 180-600mm f/5.6-6.3 telephoto for immediate access for when the targets move closer but within the permitted distances regulated by the park. In my 4Runner I also carry the Z 600mm f/4 TC, which is the lens I’d prefer to use if I can fill the frame and also carry the Z 400 f/2.8 (which rarely gets any use due to distance and set up time). In my bag I also carry the Z 70-200 or Z24-70, mostly for landscapes. In your situation I would definitely carry the 600 with a 1.4 TC, the 180-600, and the 24-70, or similar lenses. Discounting my 800, these lenses get 98% of the use. The only time I was able to get very effective use of the 400 was during the big horn rut and one occasion with elk along the Old Yellowstone Trail. I‘ve tried every other combination over the year’s+ time and for me, it’s been the most effective combination. I use a tripod extensively with the longer lens to minimize shutter speed as much as possible to decrease ISO which helps me diminish noise and increase detail. Many shots, if not most, end up being taken from the road because of limitations imposed by the park, but I also get into the fields, especially in the Tetons when seeking moose shots, and a light carbon fiber tripod with a fluid head Or Wimberely gimbal is the way to go in my humble opinion.
As far as your concern with the 180-600 having to stop down to f/8, that has not been my experience. It’s a telephoto so it will not be as crisp as the 600 or 400 prime, but it’s one very good lens even wide open. I may go to f/8 if I have the light but that’s only to increase my depth of field.