I have shot with both the 120 lenses on the Hasselblad & Mamiya ( not the D lens ) & there about the same. Really you are comparing Fugi vrs Mamiya here. I have shot billboards with the old Mamiya 80mm lens along with the old 150mm, very sharp. Each to their own & there has been plenty of debate over Hasselblad vrs Mamiya over the years.
I don't doubt the mamiya lenses aren't sharp I guess most modern lenses are sharp, even sigmas, but in the realm of medium format, rightly or wrongly the mamiya afd was always condsidered the bargain basement medium format camera and it was the tactile feel and build quality of the lenses, the body and the grinding noise of the autofocus that gave it that reputation.
It also didn't have that stellar of a reputation in rental departments and once medium format went autofocus the first two choices were Hasselblad, Contax with Mamiya a distant third.
Now that it is reskined and reworked as a Phase and Mamiya III, with a few new lenses it's improved but if it moves to Hasselblad H prices what's the point, given the fact that H series cameras are backed up in rental everywhere and you don't have to look to hard to find a good used H1 H2.
Where have all the professional cameras gone? From 5 or 6 years ago we had probably a dozen or so cameras with another dozen or so models in the professional ranks and now were down to what 4 or 5 with the hasselblad, Rollei HY6, Mamiya, Canon and Nikon.
Has Canon and Nikon just devoured the professional market leaving the rest to pick up the crumbs or has digital just leveled the field where the difference between the 645 sized cameras and 35mm is just not that great.
It is probably a combination of the two though I think the medium format digital companies had as much to do with snuffing their own market as Canon did, because with every medium format camera system there are always as many questions as answers. Where's the lenses, what's the date for for finders, right angle grips, and most importantly what's the price, the real price, not the call your dealer and negotiate price.
While medium format struggles to answer and ship the two main 35mm companies just keep pumping out new product and putting it on camera store shelves worldwide. You can buy a Canon or Nikon anywhere in the world, usually for a good price, but try to find a medium format back with a specific mount and unless your in NY, LA or London, the option of walking in and buying what you want goes down quickly.
There is one camera store I frequent a great deal. It's not the biggest, actually just a one counter store, though they sell product like water and I've never gone in when they aren't busy and even during these tough retail times had their best black friday in 10 years. I've asked them why they don't sell medium format or even the leicas and they said they're just too expensive, complicated and require too much investment for the return. If the backs were more universal they would still carry medium format cameras, but today it doesn't work that way. A pentax 6x7 is just a paperweight, a RZ 67 with a digital back turns the viewfinder into a postage stamp and Hasselblad, the HY6, even certain elements of the Phase/Mamiya are proprietary to the back/camera so the days of buy your camera first and chose your specific film are gone.
It makes you wonder if there were Kodak and Fuji digital backs, that costs $5,000 instead of 12 to 30 thousand dollars and worked on any medium format camera, that segment of the market wouldn't still thrive but the toothpaste is out of the tube, the contracts and strategic alliances have been signed and those days of buy your camera and pick your film are gone.
In medium format the tail wags the dog. The back makers have taken control over the cameras and limiting any options has not done the medium format market any good.
Bronica, fuji, Pentax and Contax stopped medium format production and it didn't make Hasselblad or Mamiya wealthy it just limited the medium format market overall.
So back to the original thread of can a Mamiya lens resolve 39mp. Sure and so can most cameras, even out of production contax, but the issue isn't the cameras or the lenses, the real question is what digital film do you use with them and no matter what anybody says, there are only two digital films, Kodak and Dalsa. The rest is just the packaging, contracts that limit the sensor shape and slight packaging variations of the same theme.
When I started digital capture and we struggled through the learning curve of icc proviles, proprietary software, updating os systems, calibrating monitors, leaning DAM, storage, backups and working files to try to mimic some kind of film look, late one night my studio manager looked up at me under a pile of prints, hard drives and calibration tools and said, you know someday we're gong to look back at a $15 roll of film and laugh at how cheap, easy and most importantly how much fun film photography was.
I am beginning to believe he was right.