I think a factor is that it's easier to make a good 80mm f/2.8 for a 645er format than a 50mm f/2 for 35mm than a 25mm f/1 for MicroFourThird. So chances are that the corners are sharper, there's less chromatic aberrations, etc. While you will be able to match DoF, FoV, etc. you will still get a different image in the end and 99.5% of people see no difference. I've shot with the Canon 85mm f/1.2L on 35mm and was blown away by it but mostly everyone I know couldn't see any difference to a Sigma 85 1.4 or Canon 85 1.8. So far I've shot m43, APS-C, digital & analog 35mm and analog 645. I think the specific look has more to do with the lens than with the camera system. Obviously MediumFormat offers also leaf shutter lenses which can be a huge benefit against focal plane shutters when shooting with strobes as you can synch flash at any shutter speed, on the other hand focal plane shutters on modern cameras have far quicker speeds available. Horses for courses. Personally I think I couldn't tell in a blind test.