Ahhh okay doky.. So my understanding of the Animatronic Generations Bell, and Avatar Priestess are all from the same Generation of animatronics in terms of capabilities and motion control, while Anna and the others are based on the design utilized in Mine Train. The Frozen animatronics had a lot of time constraint issues, and according to a few friends who worked on the project they barely completed them in time. They chose to go with a limited animatronic that would be simpler to implement in the two years they had to work on the ride. Meanwhile the incomplete animatronic you see with Belle is probably 2+ years of development based on the time frame of when they announced the ride, and they still have over a year until it needs to be ready for the public.
I hope that was easy to understand. But in short, the capabilities of an Animatronic depends on Budget and Time to get the most realistic solutions. When you limit the budget or time, you tend to fall back on previously used designed and modify them for the new designs.
