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I think it depends dramatically on which focal lengths we are talking about. Canon for example has great super teles but have always had problems on the wide end. Nikon has been strongest in the 24 or 28 to 180 area, with some lenses from decades ago still being sought after. On the other hand, Nikon hasn't updated all focal lengths at an equal pace, and the 135mm focal length specifically seems to have fallen out of favour. The 180/2.8 and 300/4 also need updating. These are all very decent lenses, but not up to modern standards, especially the coatings.
I think one reason that there was much more noise surrounding Contax than Nikon is that Contax was always an enthusiast brand, mainly going to wealthy owners, and serving as dream objects, with flashy lenses, whereas Nikon was the tool of choice for hardworking pros for decades. Only just prior to the switch to digital did Canon finally achieve some kind of parity. As such, the Nikon lenses were all rugged and delivered good image quality, but the focus was on overall performance in all conditions, not on peak performance in any particular area, such as corner MTF or elevated micro-contrast, with a few exceptions such as the Noct-Nikkor, which had peak performance in some areas, sacrificing others.
To answer your question directly, no, I don't think Nikkors get steadily better across the board. Some lenses do, but others get either neglected, or take great strides forwards. The 14-24 is one such lens. It just outclassed virtually anything else and to some extent still does, when you consider that this is a zoom which is still regularly compared to the best primes, regularly being compared to focal lengths from 14mm to 21mm. The 24mm end is not as interesting.
In the case of the 135mm lenses, they have been somewhat neglected, and the newest (only?) 135mm is a soft-focus lens from many years ago. If Nikon would apply the nano-ED-G strategy to it, they would surely be better than the also slightly dated 135L, which so many love.