That’s a 50 years old lens (release date 1977?), so don’t expect DxO to have ever measured this lens. If you call it “stunningly sharp”, surely you haven’t seen any sharp lens yet. Check Z135/1.8S on 45mpx. Not to mention that “Nikkor 200mm f/4 AI” wasn’t only about sharpness – NIKKOR The Thousand and One Nights No.87 | NIKKOR - The Thousand and One Nights | Nikon Consumer
In your comparison, you’ve probably used Landscape Picture Control in NX Studio (perhaps derived from the camera settings, which NX Studio uses automatically) or a tweaked Standard profile, while the PhotoLab version looks more like a Neutral, with much less saturation, and that affects sharpness perception. Both Landscape and Standard PictureControl use a considerable amout of a variant of unsharp mask. Hence you are comparing apples to oranges. I would say that DxO and NX Studio are on par in this case, even though NX Studio probably has some “knowledge” about this particular lens. As others said above, the perceived “sharpness” can be risen using PL Microcontrast, Fine-contrast (FilmPack license required), perhaps Unsharp mask (I think never used the latter with positive settings in PL 
). You may also use ClearView to get increased “sharpness” as a side-effect (both PC Standard and Landscape use their version). Selective Tones may also change your sharpness perception.
But these are all workarounds for old, unsupported lenses. I get “cleanest” results using supported lenses and Lens Sharpness Optimization – no halos, no rough look.
Off-topic: My oldest Nikkors are 16/2.8D Fisheye (1993 design) and AF 135/2D DC (1995 model), supported by DxO. Both gain a lot using Lens Sharpness Optimization, which is common for “unsharp” lenses. The second lens had an opinion of one of the sharpest lenses at the time, but it’s nowhere near to AF-S 105/1.4E, not to mention Z135/1.8S. That said, sharpness is by far not the only thing one should be after.
EDIT: DOF used was too shallow, so some parts are unsharp “by design”. The background was far and there was a lot of light, enough to stop down the aperture considerably. Which makes the initial question about sharpness even more weird…