Hello Thomas, thanks a lot for your explanations. They are indeed extremely helfpul and interesting for me, and they help me understand and form an opinion - although one which surprises me so much that I have trouble trusting my own eyes. Could it indeed be that lenses get applauded all over the net almost as being the new standard, while in real life situations, some older lenses are much better in the special area those new lenses are applauded for? Have I really just learnt that those super sharp lenses are indeed super sharp, but not in the focus area I'm focussing on (except in the image center)? And that indeed a lens with less theoretical sharpness and less field curvature, will in real life images produce visually sharper images, because these images are sharp in the focus level I'm focussing on across a larger portion of the image?
I have meanwhile also checked the images of the Sigma 35mm f1.4, and those of the Nikon 24-85, I have the f2.8-4 D version of this lens, so I find this interesting too. And I have that Sigma, although I only tested it for a few days, before I had to send it in for service (front focus of 15cm on my D800 and D600, and infinite is sharp about one cm before the focus ring reaches its end (Anschlag).
It seems that even with the blazingly sharp Sigma 35mm, in terms of visual sharpness, the Nikon 24-70 can compete quite well. It is probably not better, but also not worse, which I'd find utterly surprising because it is a zoom versus a prime.
Edited due to new findings
I have now compared the original images of the two 24-70 lenses. My purpose was to determine where exactly the Tamron is sharper, and where the Nikon is sharper.
It seems that the Tamron is sharper in the center, up until somewhere in the 50% range between center and border. Outside this central area, the Nikon takes over, and anywhere from 60% and further to the outside, it seems that the Nikon is much sharper than the Tamron. Which actually makes the Nikon's image look sharper overall, as actually is it sharper in a larger area of the picture, as the Tamron is only sharper in the center area, while the Nikon is sharper in both outer areas.
The Sigma 35mm also seems to get softer around the edges, but the softness sets in much later, at maybe 80% of the distance from center.
Am I on the right track?
Thanks for letting me know!