P.S. Sigma has asked if they can send me a second copy of the 135 ART to see if it tests as being sharper for me, and I have agreed. I will be following up in a few weeks with those conclusions.
P.S. Tamron is doing the same with the 70-200 G2, as I criticized the performance at 200mm as falling behind the Canon 70-200L II, while some others found the opposite to be true (including Roger at LensRentals).
I guess my point is that sample variation does exist in the real world, but that we are also doing a lot of hairsplitting at this point. These lenses are very, very sharp, and when you compare them to other very, very sharp lenses not everyone gets the same results.