Surely with the 200-500 zoom, it would be easier to start at 200mm to locate the subject within the viewfinder, then zoom in to frame and compose.
A separate finder could be useful for long telephoto primes, I can imagine with such a small angle of view, it would be difficult to frame the subject in the viewfinder. On the Nikon 2000/11 reflex, a small sight was built into the handle, but they didn't provide this feature with other long lenses.