I think there are other variables to be considered. I have and use the RB67, a Mamiya 645, a Fuji GS645, and the Mamiya TLR system. Prior to owning the RB, I used a Kowa 6.

The RB is my "serious" camera. Always on a tripod, and with interchangeable backs, I use it much like others use sheet film. (other than the individual sheet development). Second, though, is the Fuji. Usually used handheld, it yields negatives very comparable in most prints from the RB. It just has a different "look". However, I'll take the Fuji places I won't bother with the RB.

They are all tools, and you have to use the one that's comfortable for you to use and meets your needs. Size, weight, lens selection (or not - see: Fuji) and shooting style all figure in.

A carefully exposed and processed negative from 645 can be beautiful. In fact, I am having good enough luck with T-grain films in 645, I've started to shoot some in 35mm just "to see"! YMMV