I doubt that Nikon or indeed anyone else could make a better lens than the 100-400 II. In fact it's not really a lens, it's a bleedin' miracle.
Maybe in five years. The 100-400 II is as far ahead of anything else in its class today as the Nikkor 14-24/2.8 was in ultra-wide world a decade ago. Canon
did improve on that one ... eventually ... after many years of work and lord only knows how many R&D dollars, and at a mind-blowing price. $3000 for an ultra-wide. Strewth!
But your point about the cheap little 200-500 is a good one. It is apparently way better than anyone would expect for the money. Why would you buy an expensive, mediocre 80-400 when you can have a cheap, decent 200-500?
Landscape folks? Are you kidding? My best, most productive landscape lens is the 100-400. I use it all the time. Love it! The only thing I don't like about it is that it's just slightly too long at the short end, which is why (don't tell Tea!) I just got a 70-300L as well.
(These were all with the old one, mostly with a 1D III or 1D IV. The new 100-400 is even better. I can't wait to do some serious work with it.)