I was wondering because the way you talked about the RF 100-500 in that post made me wonder if you were politely dissing it. I wasn't sure, so I asked.
If that was the case, I was going to reply how it is my favorite lens so far, and reasons for that.
But based on your reply, I obviously mistook your intention. I would also agree that it is "worth it if one could".
So, as Rosanna Rosanna Dana once said, ... "Never Mind!"
It's small and light, which is a huge plus when you go out hiking with the camera or hand hold for a period of time. The Sony 200-600mm, fine lens that it is, is heavy. Many can manage it, as some do hand holding a 600mm f/4. But, the 100-500mm, and the 100-400mm II, are a lightweight pleasure to use.
The Nikon 500mm f/5.6 is slightly lighter. I suspect Canon could produce a 500mm f/5.6 DO that is 100-200g lighter than the 100-500 L, but that might not be as compelling as the PF if you saw a 100-500 L and 500 L both about $3000 next to each other. A 600mm f/6.3 on the other hand would also be light but give something not existing, might even be lighter than the 100-500.