I have a suspension that with the 500mm we are close to the point that the additional pixel density will improve your reach or resolution. I know this is purely anecdotal but when I bought the 5DsR I did tests with all my lenses. I saw real improvement with all my zoom lenses, but the big white lens the improvement wasn't as noticeable. It is the sharpest lens I have and I thought maybe it was because the lens was getting close to the point that additional MP wouldn't improve much. Maybe there are diminishing returns as you get more density. Overall I just felt the 500mm didn't benefit nearly as much as my other lenses.

If you have a 5DsR you could test and see how the M6 II compares.

FWIW my brother just returned from Yellowstone. In West Yellowstone restaurants were hard to get in due to Social Distancing Rules. Many hotels and motels were closed, the ones that were open he was able to get a room and the rooms were discounted. The park was not packed with a crowd, he said it wasn't bad. Last report I received from him he had only seen a few bear at distance, no wolves, sheep or moose (Moose is the rare site in the park). If I had been with him and had the 500mm it sounds like there would have been little or no opportunity.

Focus on the landscape equipment, take the 500mm just in case.
Typical photo opportunity:
Yellowstone 2012 (1 of 1)-2 by hdnitehawk01, on Flickr