The question for me if comparing the lenses alone is whether the Hasselblad lens produces a more or less technically sound image in a 10x10 in. or 15x15 in. full frame print than the Mamiya lens does in an identically-sized print. (10 in. and 15 in. prints are the most common sizes that I print from medium format.) The answer is probably that in this case the Hassy lens produces slightly more technically sound images of test charts, but when it comes to standard pictorial applications, the differences may be much harder, if not near impossible, to spot at these degrees of enlargement.
When it comes to making a non-square print, I would say that the advantage goes to the Mamiya...but this time the difference is a bit more noticeable. Unlike in the above example that I gave, in which a Mamiya frame is cropped to make a square print, and there is no resulting difference in final magnification, when the Hasselblad frame is forced to conform to the Mamiya's ratio, there is a difference in magnification. IME, this is not very visible in 10 in. prints (about 4.5x enlargement for the Mamiya, and 5.25x for the Hassy), and it begins to become apparent with 15 in. prints (about 7x enlargement for the Mamiya and a little over 8x for the Hassy), though not different enough to warrant the slightest bit of concern in a standard pictorial application. I would only call the difference "easily noticeable" in prints larger than 15 in., which I almost never make. Even then, the differences would not be great enough to warrant any concern from me, as both would still be very technically sound.
Either one of these lenses should be able to produce technical results satisfactory for almost any use I have (and that most of us have), whether cropped or printed full frame. I'd choose between the two systems based on almost anything but image quality.