With respect to the effect of a flywheel, I believe (my physics are quite rusty, about 40 years rusty) the important effect is Angular Momentum and the Moment of Inertia, both of which are directly influenced by angular velocity. Moment of Inertia also feeds into the torque of a rotating object, once again angular velocity is directly related to torque. The flywheel acts as a torque multiplier, something the relatively small motor needs. Also, keep in mind the VPI flywheel is turning at a higher speed than the platter. I can't speak to the dual motor flywheel, but I have the single motor flywheel and while I haven't measured it's speed (and couldn't find anywhere in a quick search that listed it) it is several times that of the platter. This further increases it effect beyond what one might expect.
Now if only Brf would chime in we might get a more definitive answer!
Now if only Brf would chime in we might get a more definitive answer!