I just looked at the photo in the provided link. In my humble opinion, you cannot judge lens symmetry at this distance. It could be decentering, or it could also be that right and left objects are not exactly at the same distance to the sensor plane. The only way to check, and this is what I did with my 16-35, is to take a photo wide open at infinity and compare right/left side. The photo should be ideally a cityscape because you can easily check sharpness with buildings and man made structures.
I did the same test with my 28-135 and it was supersharp in the same right corner at the same f-stops where the 24-70 was very unsharp.
The test also revealed that the 28-135 was a little sharper on the right side. Compared to the differences showed with the 24-70 it was nothing to worry
about.
I think this is an indication that the test is OK, and shows the problem with the lens precisely enough.
I took 25 pictures or something, some of them was focused manually at the rightmost coffee-box, and they turned out to be the sharpest both at the right and the left side.
I took some pictures this summer including distant buildings, same there, fussy on the right side.
So, if you can talk yourself into that the test is good enough, how bad would you rate the defect?
I wonder how many months it will take this lens to go from Norway to Japan and back again.