That is a good point, I redid my test, this time positioning my subject at an angle to reveal any shift in focus. I also focused the RF 100mm stopped down to f8 by holding the aperture preview button and moving the camera accordingly.The RF 100 is known to suffer from focus shift, and macro distance at f/8 with a flat subject is where that would be evident.
Again the 24mm is on the left, the 100mm on the right. While not being as extrem as in the first example, I would still consider the Rf 24mm to be a bit sharper.
I am glad it has IS, I find this gives it that little extra in hand-holdability. I went hiking yesterday and took the 24mm with me and after sunset I was able to hand hold the camera for 5s. The images are not perfectly sharp, but absolutely useable.It's funny how so many of the lower end lenses have IS now. Especially given some bodies have it and this particular lens is so wide. I have the Sigma Art 24 F/1.4. This looks appealingly light in comparison, but also a little boring.
I also wished that Canon would've released a 24mm 1.4 or even better 1.2, since I'm a big fan of shooting wide but also shallow, but so far I'm happy with the performance of the 24mm 1.8 and it will be a good lens to entertain me until there is a faster option.
Here is an example image from yesterdays hike, shot with the 24mm, wide open at f1.8.