I have a pair of C220's and 6 lenses: the 65, two 80's (one old style chrome one newer black), the 105, 135, and 180. I'm also with 2F/2F here in that all these lenses are top notch as far as I'm concerned. I also have a Hasselblad 503cx with a set of 50, 80, and 150 lenses. I don't find the Mamyia glass to be lacking at all by comparison. If you were to put both on a bench and measure the performance, you will see differences. In real life, there are many other variables affecting the look of the final image making the bench test results less significant.
The 105mm Mamiya lens is probably my favorite of the bunch. Mine is old style one in the chrome housing and is supposed to be slightly inferior to the later models in the black housing. Maybe, maybe not. All I can say is that I'm very happy with the performance of this lens.
Direct comparisons of field of view between 35 mm and 6x6 are not very useful because the aspect ratios between the two formats are so different. The 80 mm "normal" focal length for 6x6 feels very much wider than the field of view cast by a 50 mm lens on the full frame 35 mm format. The 105 feels just about right.