It took a long time for Nikon and Canon to have complete telephoto Prime lenses collection for their mirrorless Z and RF mounts respectively but looks like it was worth the wait. Since we have an almost complete coverage now starting from 400mm to 1200mm (well Nikon doesn't have a 1200mm yet but that's OK!), let's look at which manufacturer was more successfull in keeping these lens compact and lightweight.
Looking at the photos, I say overall the Nikon ended up with more compact designs for the comparable focal lengths, do you agree? Keep in mind that the Nikon 400mm and 600mm lenses have built-in 1.4x Teleconverters which gives a huge advantage over the Canon counterparts.
Nikon Z 800mm vs 60mm vs 400mm vs Canon RF 1200mm vs 800mm vs 600mm vs 400mm Size Comparison
(Click on the image for the larger version)
Feature and Specs Comparison
Recommended Cameras to take full advantage of these monster lenses: