Sample-to-sample variation has probably always existed in camera lenses, but, it’s much more obvious now that so many people are pixel peeping their images at 100 or 200 percent. It’s good to know the ultimate capabilities of your lenses, but sharpness is just one facet of imagine quality and image quality is just one facet of a good photograph. So, overly obsessing about sharpness distracts from the ultimate goal of creating a great image.