A Canon RF 7-14mm f/2.8-3.5 Fisheye Zoom is Coming Soon

[EOS 4 Life]

Primes are restrictive but the 200-800 only resolves to about 650mm (per tests in this forum) and beyond that it just makes the image bigger without any additional detail resolved. You'd do just as well with the Nikon 180-600 and then up-sizing in Photoshop or with an AI resizer. Or the Sony 200-600 for that matter.

That is not the resolution.
That is the magnification at standard testing distances due to focus breathing.
The 200-800 exhibits a lot of focus breathing with the benefit of being able to focus really close.
That being said, it is not the sharpest lens at 800 mm.
Stopped down to F11, it is about as sharp as the RF 800 f/11 though.