I have a Zeiss Ikon in place of your Mamiya-Six, but also have a pair of C330s and a Rolleicord, and I can't say you're faced with an easy choice.
Of my 3 the Rolleicord is probably my least used, but I tend to reach for the C330 and its extended focus range unless I have a reason to skip the extra weight. If a C330 hadn't been the first TLR I got into I don't think I would put up with the weight and bulk if I picked one up after years of using and exploring a TLR as light and handy as a Rolleicord.
If I'm skipping the bulk/weight of the C330, then I'm more likely to skip all the way down to the far more compact folding rangefinder, but mine is a HEAVY chunk of material. [It also is the weird one that does 11 frames on a roll...]
Best bet on something like this if you insist on downsizing might be making a pros/con chart and try to establish a points system to rank them, but I honestly don't find they have enough of an overlap in use and images to say that any one of them fully 'replaces' the other.
I use my rangefinder far differently than I do either of the TLRs. The range finder works from eye level, the TLRs consistently work from lower down. The views I sight with them are just different. The mood I'm in while working with them are different, and they have entirely different values to me.
The Rolleicord is a lighter and more specific use TLR. My C330 with a handful of lens options is a bit more general with its greater flexibility [at the cost of a fair bit heavier bit of kit to lug around.] But they're both cameras for "I'm planning to take photos".
The rangefinder however tends to be my "I hope I get to take photos" camera, and tags along when I'm out doing other things.
The pros/cons chart is a good idea. Thanks!