I would be a lot more interested in a 200-500 f/5.6 than an f/4, just considering weight and cost. I’m not interested in carrying a monopod at this point in my young life.
But, in the Canon world with the well established and /as far as I know/ well loved 100-500mm f/4.5-7.1 L, is a 200-500 upgrade (constant aperture, but.. better through only part of the range, and likely to accept an extender throughout the range, unlike the 100-500 where the extender can be used 300-500), enough? I think it would be for me, but I don’t have a 100-500?