Having a stacked yoke is not all bad:
A lot easier for shipping; two long boxes in lieu of a huge rectangular box. Make's a big difference when you're grounded wayyyyy out there. Also the issue of tip path being different for each yoke has no negative effect on ride quality. The Bell 430 also has stacked yokes and has one of the smoothest rides of any helicopter. A lot of the issues with working Bell 412 rotors are related to either bad rubber (seperated/too old) or bad blades (too many repairs/paint touch-ups)
As for the weigths added to the M/R head, SPA (simple pendulum absorbers) weights, they are there for the 4/rev. They were not there originally but were added aerly on to help control 4/rev. Same type of device can be found on other four bladed system (BO-105/BK-117).