50mm medium format lenses designed as portrait lenses?
Never heard something so silly.
The angle of view of 50mm on 645 cameras is the closest to human angle of view/visual perception.
It is a very general purpose focal length. That said a fast (relatively fast) 2.8 50mm lens is nice
for environmental portraits, but this story about sharpness only being important in the center
for portraits is not true. many many portraits with wider lenses are taken with the subjects face far from
the center of the frame.
Also just go and look at the brochures of nearly every fast 50mm 645 wide angle lens or (35mm 24x36 lens).
The sample photos are landscapes.
Another thing I have found is that wide angle portrait work is really much better with a tilt shift lens.
The manufacturers can talk it up all they want, but even resolution or at least and smooth gradual fall off in resolution is important for wide angle lenses
be it portrait of landscape. With a wide angle lens features are smaller and hence to be described well need more resolution.
While most Mamiya Phase lenses are excellent when it comes to sharpness there is not an across the lens range consistency.
For example bokeh with the 150mm LS "Schneider" lens is not nice, however the Mamiya 150mm 2.8 is remarkably nice.. I would say
one of the all time best MF lenses.
My point is that the 55mm 2.8 LS is nothing special at all and grossly over priced for what you get.
On the other hand the older non LS Mamiya 55mm is really quite good and excellent for the price.
$ 800 vs over $ 4,000.
I have owned the Mamiya 55mm and tested the 55 LS.