I was in Yellowstone in 2019 with my longest lens being a 70-200, and it just wasn't enough reach.
In 2021, I was back in the park, and once again, the 70-200 was my longest lens, and as such, I didn't even bother photographing any wildlife. I was originally in Colorado, and when it looked like my guide situation for my climb was going to fall through, shoulder season with fall fast approaching, I called my local store back in Alabama to see if they still had a used 200-500 that was sitting on the shelf when I left, and I was just going to put the money into that and try to give Yellowstone better attention on this trip. The climb did come together, though, so that money was spoken for,
and I once again rolled into Yellowstone with woefully inadequate glass for wildlife.
I did get this timelapse, though, so I was happy enough. 14mm, fwiw.
Yes, I've been able to get reasonable photos of elk and bison with a 70-200 and even a 24-120, and would have had a macro photo of a bull elk with a GoPro, had the battery not been dead, and speaking of dead, I was lucky that I wasn't. But, you have to ask yourself, "when am I, realistically, going to get back there again?" Yes, I know it's more money, but I think longer glass is money well spent if going into the park.
I recently picked up an 80-400 around the first of the year, and I'm so glad that I did. While the 200-500 might be the better lens for wildlife, the 80-400 has turned out to be an absolutely fantastic walkin-around lens.