That's an S2 they are using by the way, two generations old (S2, S006, S007).
I find it odd that they used beauty portraits to test system sharpness. Isn't harsh, clinical sharpness the last thing sitters want?
I prefer the smoother look they achieved with the Leica files, but you could match that with the Canon files by dialing-back the contrast and sharpening.
I don't have much of a stake in the comparison, as I am not a candidate to switch to Canon, but as a Leica S user, I would say that it is not wise to shoot at f/13 or f/16. I am not sure if it is diffraction, or just lens performance, but the 120mm S macro is significantly better at f5.6 or even f4 than it is at f/13 or f/16. I generally don't shoot above f11 on the S unless I need the depth of field...5.6 or 8 is usually ideal, but in my experience 2.8 would be sharper than f13 of f16...the 120mm macro is insanely good. Keeping the shutter speed high (even with mirror pre-release) can make more of a difference than aperture in pure performance on the S2.
Either way, I would expect that the 5DsR equipped with a great lens would outresolve the S2 at small apertures...it is a 50mp camera vs 37, and the S2, as wonderful as it is, was introduced seven years ago, vs the 1.5 year old Canon. And yes, the S needs a resolution update, and as a shooter of it, I would be the first to say so! But it is great that Canon shooters can now access this level of resolution for a reasonable price.