I love using telephoto lenses to isolate areas of interesting light, color, shape, or texture in the landscape. I also love using them to compress layers in the landscape to create telephoto-stacked scenes. Unfortunately, Fujifilm has not yet released a lens that is longer than 250mm, equivalent to 200mm on a full-frame camera, which leaves me needing more "reach" from time to time.
There are some limitations to using the Canon lens on the GFX medium format camera bodies. The Canon lens is designed for the smaller full-frame sensor which unfortunately means that it doesn't fully cover the larger sensor in the GFX bodies. The result is that there is fairly significant vignetting in the corners of the image and depending on the focal length the lens is set to, it's common to see less than optimal image sharpness on the outer edges of the image. I typically use this lens with the camera set to "35mm Mode" which still gives me 61 megapixels of information, the same as what is found in the Sony a7R IV and a7R V camera bodies.