I think the issue here relates less to optics than film size. Any half decent MF camera will produce images that look far smoother and have miles more detail than a print of the same size fom 35mm. My comparisons come from Rollecicord/RZ67/120 back on 5x4 shot negs compared to Canon Eos lenses and my Ricoh GRl (which as you probably know has a lens good enough to be indistinguishable from a very expensive german prime lens at one stop down and is avilable in M mount). This however, is not the point. The 35mm negs enlarged to the same size look grainier, have coarser granularity and far less detail. However, this look is often very appealing and is sometimes preferable to the (at times less atmostpheric and more sterile) creamy reality look of MF.
The bottom line is that my best 35mm does not come close to approaching my ancient Rolleicord Va in terms of detail and tonality. Nor would I want it to.......Portraits of children in 35mm (esp if lith printed) have a unique quality for example (Cheryl Jacobs might agree) that would disappear with a 6x7 neg and slow film. ANother issue I think often forgotten is the conditions of the shot. A leica 35mm shot at f5.6 and 1/60 hand held is not going to look any sharper than that shot on lesser optics, let alone one on MF. I think they are completely different beasts which cannot really be compared. For those shooting on HP5 and TriX, optical benefits are lost as the films are relatively coarse, though contrast may be superior with the Zeiss/Leica optics. I have all but stopped using sslow films with 35mm, as if I want tonality and detail, I go straight to a bigger format assuming it is practical to use. I use faster films (HP5, Neopan 1600) and sometimes print on a condenser with 35mm to get sharp gritty grain. I would love to own a leica (but not to pay for it), but with HP5 my Eos kit produces great results. I would want a Leica for its size, unobtrusiveness, quietness and mechanical reliabiliy.....but would not be loading it with Acros developed in perceptol!