I appreciate the challenges there must be to create a costume that can survive on stage and provide maximum mobility for performers. You have my respect - I can scarcely handle a staircase wearing my armour.
The Disney armour veers a bit off course because, like FX armour, it's an artistic interpretation of the stormtrooper. It hits all the big features, but it lacks the troopers' essence. I would think audiences would pick up on this.
First off: lose the helmet. Can't sugarcoat it. It looks like a Rubies. The eyes and dome shape are off. The bridge of the nose/snout seems pushed in too.
The breastplate is off in a curious kind of way. The sides are cut too wide. Reads more like a tank top than a breastplate. And the cod piece is kind of cut too wide as well. The overall effect is that the troopers look more like they're wearing white leotards than armour.
(Probably not great for instilling fear in the masses).
If these suits have to be designed for maximum mobility, maybe they ought not to be made of hard plastic (heresy, I know).
Go for 100% accuracy, but reconsider the material. Perhaps a semi-rigid plasticized foam with great memory might fit the bill (at least for the armpits and hips). How it's done, I leave to others of a higher pay-grade than I....
Good luck...