Bill,
Convolution sharpening techniques are a separate issue. As you know, DXOMark, for example, do not convert the RAW images prior to taking their measurements because the quality and characteristics of the converter would cause a bias.
I'd say if one has raised one's resolution standards after getting used to the increased resolution provided by the 5DS(R), then one might be disappointed when comparing an F22 shot with an F16 shot using the same camera.
However, if one has frequently used F16 with a 5D3 and found the resolution quite acceptable for reasonably large prints, but has avoided using F22 with the 5D3 because the results are noticeably soft, then the 5DS(R) at F22 should produce more satisfying results than the 5D3 at F16, when the image is downsampled to the 5D3 file size, and whenever maximum DoF is desired of course.
I have assumed that the camparison crops shown in the review are of an area that is in focus. It would be interesting to see how much more detail is visible in the 5DS shot (at F22) in areas of the scene furthest away from the plane of focus.
I don't see any problem using a textured surface for such comparisons. This relates more closely to the nature of 'real-world' examples that most people encounter in landscapes.
I recall a few years ago comparing the last Canon camera I bought, the 15mp 50D, with the previous model, the 10mp 40D, photographing a banknote fixed to the wall. It was interesting that the 50D at F11 was about as sharp as the 40D at F8, using the same high quality prime lens and downsampling to 10mp. The 50D at F16 was also as detailed as the 40D at F11, after downsampling. However the 50D at F22 (if my memory serves me) was not quite as detailed as the 40D at F16. It was very close, but pixel-peeping at 100% and even 200%, I had to admit that the 40D at F16 had a very slight edge.
Now the 50D has only a 50% increase in pixel count over the 40D. The 5DS has over a 100% increase in pixel count over the 5D3. I can believe that the 5DS image at F22 really does have as much detail as the 5D3 at F16.