Well I can carry 65, 80 and 135mm and Mamiya C330 15miles in medium sized gbag and not notice it at end of day of city streets.
The RB and three lenses and spare back needs all day in coffee shop way points, working from Billingham
A blad kit is still to heavy for 15 miles
When you fire the 12th or 10 frame the C330 is faster to reload compared to insert camera or back. I can reload on fast walk if the sun is behind.
The spare back allows another 10 or 12 but then you need to reload twice and juggle.
Only lens changing is a handicap with the C330.
I still have 220 for another few months so the insert cameras will be at bigger disadvantage with 120 only.
For faster shooting I need three CanonP (35mm) and three lenses.