I regard the Tamron 15-30 f2.8 VC as a better option over the Nikon 14-24, unless if weather sealing is important to you.
Why the 200-400mm? Why not the 200-500mm?
200-400 is a constant f/4. It appears the OP is obsessed about maximum apertures.
A lens that has a constant maximum aperture value throughout its zoom range is, in most but not all cases, a very simple shorthand way the manufacturers (plural) use to differentiate/signal that said lens is not an entry-level or low-level, nor a mid-level lens. A zoom lens that has a variable maximum aperture indicates that there have been "compromises" made with that lens, either compromises in size, weight, performance, durability, and the anticipated end use, or even all of those things. Almost every single Nikon-made zoom lens that has an f/2.8 max aperture is, or was, the absolute BEST lens Nikon had ever made in that category, when the lens was released.
Maybe the OP is obsessed with buying the best lenses available? Those lenses ALSO happen to typically be built to withstand 25-40 year ownership and use expectancy.
There's a simple reason the 200-400 f/4 is on the OP's wish list...it was, when introduced, the top of its class in the modern era. Right now, I've seen 200-400 VR Nikkor lenses selling for about $3200 to $3499 here in my city, on the retail, in-store, used market. Same situation with the 14-28 f/2.8-G...when it was introduced it was **the best performing** wide-angle zoom ever made, and it was/still is significantly better than MOST older, wide-angle primes made by Nikon, Canon, Contax, and Zeiss...
The 14-28/2.8 is MARKEDLY better than Nikon's older 16,18,20,24mm primes. Markedly better, in multiple metrics.