I used an older 50mm on the RB and found it to be rubbish (with film); given digital’s lack of forgiveness, the lens would likely be unacceptable to many users. So I switched to a Bronica SQ-A which had good to excellent lenses. Best Mamiya 6x7 lens I ever had was the 140 macro—terrific!
Interesting that you can use old Bronicas today w/digital backs.