Simply put, the 35mm lenses for Leica are wide-angle lenses built to project a wider angle. The Fuji may be a 35mm lens, but it projects a narrower image. So, we're comparing lens projections for one lens built for the camera and two that are not. If I put on a 35mm LF lens, it would make the comparison even sillier, because that 35mm lens is made to project an image muuuuuuch wider still, and which, depending on the film size, could be anywhere from 16mm (FF) to 23mm (FF).
That, and the LF lens wouldn't get close enough to the sensor on the X-T1 because of the massive flange distance of the X-T1 and adapter.
It IS fair to compare a 35mm built for a certain film size with another 35mm built for the same film size. That makes total sense. For APS-C, the Fujinon is a 35 that isn't a wide angle. It is a 'normal' because of the size of its projection circle. But you know that already.
I am doing no favours to either the Canon or the Leica. I understand the argument: sharpest in centre... but if the only thing you look for in an image is sharpness... and better yet, I used an adapter. It is a Hawk's Factory, which previously I derided for being off-centre, and in parts, not perfectly parallel to the sensor. It also has internal reflections which I have tried to baffle away. I am doing no favours to any non-X lens. As to drop off in corners in a FF camera... you understand of course that by doing so, the lens would then be a wide angle, equivalent to the 23mm on the Fujifilm, so it would be a completely different comparison anyway.
And, you don't know that. The Canon is a 60 year-old lens. The Leica is 20+ years old. Both are built for film, so it is likely that they have more problems at the corners on digital, but without first testing them on their native mounts, I wouldn't dare call that definitive. Again, which is why it is silly to compare any lens built for a different sized sensor on a smaller sensor. The lens wasn't intended for that use, it may be on a poor adapter, its alignment may be wrong even on high quality bellows. There are so many equations. But I did it anyway because it's what I do. I love doing silly comparisons. And make no mistake, it was silly.