That's... a bizarre question. The implication being that Mamiya decided it maybe wasn't going to do QC any more once it went to electronic bodies or something? Why would the quality be poorer in the newer, improved product?
Many of the designs are optically identical to the latest RB K/L versions (e.g. 65 M-LA, 180 W-N, 250 APO, etc); the only substantive change being the use of an electronic shutter instead of clockwork, which makes your exposures more accurate.
Going to the RZ gets you the 110/2.8 and 50 ULD, neither of which were physically possible on the RB due to (IIRC) the physical size of the throat in the mount. IMHO the 110 is wonderful (I use it 80% of the time) but it is certainly not the sharpest RZ lens by any stretch of the imagination.