R22 life limited components at 2200 engine Hobbs:
Engine--same as G2
MRGB overhaul (replace main gearbox pinion)--similar to G2
TRGB overhaul (replace gear set and pinion)--similar to G2
Some fasteners: coning hinge bolt, pitch horn screws, TRB attach bolt--doesn't seem like that big of a deal
The big differences: MRBs and TRBs are life limited on the 22 (and 44, and 66). Yes, those are expensive.
6 months for an R22 overhaul? That's just ridiculous. It doesn't take anywhere near that long unless you don't order any parts ahead of time and your gearbox overhaul shop is sloooooow. All of the R&R steps are the same, G2 or R22: both gearboxes, engine, blades, misc. stuff.
People continue to charge more per hour for a G2. Therefore, unless the machine can simply command more profit, it has to be more expensive to run, Robinson life-limited components not withstanding.