I've directly compared the Zeiss MTF's for the Contax 645 and the Hassy V-system lenses (and am lookingat the them right now), and in virtually all cases the Contax lens was faster and sharper (or just as sharp).
You have me at a disadvantage in that I'll be away from my computer for the next week and so don't have direct access to my files. However, perhaps you could post the relevant MTF charts so that the forum can make up its own mind?
But let me first clarify a few points. Your original post was that "The Contax 645 lenses are generally sharper and faster than their Hasselblad equivalents". I'll concede the "faster" part, and so didn't comment on that, but I disputed your point about "sharper". In my reply I said, "But they (Contax) just aren't that sharp compared to either the Hasselblad H system or the modern Hasselblad V system lenses like the 100mm, 180mm, or 250mm/350mm Super Achromats.
So let's take a practical example. Assume a photographer is looking for the sharpest medium format telephoto lens, and narrows his or her choice to the 180mm Hasselblad V, the 150mm or 210mm Hasselblad H, or the 140mm or 210mm Contax. As I say, I don't have the MTF charts to hand, but I did exactly this exercise when I was deciding what system I'd use for a P25 and from memory the answer was clear. All the three Hasselblad optics were extremely close, and the two Contax lenses trailed behind. But perhaps you could post these five MTF charts and if I'm wrong (which happens all the time) then I'll freely concede the point.
Following this same pattern assume our photographer wants the sharpest possible wide angle lens, so let's take another five options. The 40mm IF Hasselblad V (not the older 40mm CFE, it's an important distinction and one I previously made), the 38mm CF 903SWC (not the 38mm CFi 905SWC, again I emphasised this in my previous post as the 903SWC uses magnificent optical glass, unfortunately it contained arsenic and lead and is now prohibited), the Hasselblad H 35mm, and the Contax 35mm and 45mm. My recollection is that it's the two V series lenses that set the standard, with the other three showing similar performance amongst themselves but falling behind the V series candidates. However, if there's any way you could post the charts then we'll open the debate to the collective wisdom of the forum.
Regarding your observation about the Zeiss/Sinar lenses, yes I agree they look incredible, as does the Rodenstock Apo-Sironar Digital HR lenses. But it's a bit disengenuous of Zeiss to describe them as "medium format" when they only appear to have a 60mm image circle. Okay for me using a titchy little 37mm x 49mm sensor, but on this basis we should judge the all the lenses only out to 30mm from the centre. Which incidentally was exactly what I did when I was deciding what system to use with a digital back. In fact what I've found from experience is that as long as I'm using lenses that deliver about 40% MTF for the 40 lppm curves out to 30mm from the centre then I'm delighted with the results on a P25. It's sobering to consider however that with the denser pixel count of the latest 39MP backs even this demanding criterion probably isn't enough.