It's time stitchers start to fix this mistake: calling the no-parallax point as
nodal point when it actually is the
entrance pupil, which can be a very different location on a lens.
E.g. (N1=nodal point, EP=entrance pupil):
The author also attributes to stitching the absence of distortion, and to UWA lenses ugly distorions, when distortion is going to exist whenever we map a large FOV on a single flat image. The kind and appearance of this distortion depends solely on the FOV and the projection chosen, not on the nature of capture (stitching vs UWA). A rectilinear projection (the only valid for proper rectilinear arquitecture photography) will end in stitching with exactly the same distortion as using a single shot on a rectilinear UWA. On the other hand a rectilinear UWA capture can be "re-projected" (using stitching software is an option by the way) in any other kind of projection getting the same result in terms of distortion as any given stitch.
No free lunch: every type of projection has strongholds and weaknesses; rectilinear is usually preferred when straight elements need to be respected as linear, cylindrical works fine for nature landscapes because it doesn't distort the left and right ends more than the centre, etc...
A good resource to learn about projections, no matter if we don't use that software:
PTAssembler Projections.
Regards