Tim, with all due respect, can't fetch the point out of such kind of claim as you did, namely: "My personal opinion is my Mamiya rb67 is better than any Leica optically, it's just not as convenient."
IMHO, this is exactly as to claim that someone's 40 ton truck is better then someone's family range Toyota (you may replace Toyota by any other regular private car). Those things just of totally different cathegory, may only compliment each other, but certainly not to compete with each other.
You obviously meant Mamiya RB lens is better then Leica lens, right ?
If this is what you intend to imply, I cannot agree with that either...
We all realize that the larger is the format, the lesser enlargement needs to be performed for given size, hence the less are sharpness requirements from the lenses of larger formats. A good/best medium format lenses may actually be somewhat less sharp then best 35mm lenses, yet still provide better percieved quality of final print per given enlargement, just thansk to achieving the final size with much less enlargement of the original.
However, I'd expect best 35mm lenses technically outperform those in larger formats and this is OK for me bearing in mind the original format (perhaps Mamiya 7/7II lenses can be exceptional on sharpness according to what I keep hearing). Certainly, on a stable tripod, aimed with proper technique, there are good chances nearly all, even inexpensive MF systems will allow finer enlargements over Leica (or other high quality 35mm brand), but no matter how better the final results can be, if no appropriate technique (tripod, proper scanning, etc...) is going to be applied - I pick Leica (or other ample 35mm tool).