I hear what you are stating, of course both settings are ideal and since the 19mm has rotation between the two settings as well it doesn't get any better for FX,,,
Agree the price hurts even though it appears the lens is a mechanical marvel as well as optical,,,
Price is equal to buying an additional D810 and two samples of the 20mm 1.8 AFS for dedicated 'one shot' two images (Two cameras two lenses) stitching ready images,,,
Then the nodal point is shifted,,, damn