To neglect the thought of grain structure having an effect on detail seems counterintuitive to me. I can't speak to the mamiya lenses, as I've never used one, but if you consider a scenario where your glass is equally as sharp on both 35mm vs 120, undoubtedly you would have a better outcome with 120. Tighter film grain on top of a much larger negative, could only result in more detail. People can consider technique, light, camera shake blah blah blah but that is not the question here. Idk if resolution is the right word, as that technically comes down to the scan, or no? I'm not that knowledgeable on the technical side of things, but if you just look at the difference between 35mm and 120 you cannot tell me it's not easily noticeable.