As pointed out already the apparent light falloff on the ground glass is normally not what one will get on film.

I think the light falloff is normally (cos v)^4, cosine to the 4th power of the angle of incidence on film. With v=45 deg (corner of a 6x6 neg with a Zeiss Biogon 38 mm) this would be 1/4 or 2 f stops.

When I see pics taken with Hasselblad SWC published on flickr and other places I usually see a clear light falloff. (I don't have an SWC myself).

Some fancy modern lenses may partially compensate for this. I happen to have a Zeiss Distagon 40 mm, and with this the light falloff seems to be smaller. (As far as distorsion and shaprpness it is of course outperformed by a Biogon).