A heavy platter like that used on the Final Audio, will lower the rates of deceleration, acceleration. High inertia reduces the magnitude of speed changes, it does not eliminate them.
The connotations of the words "immediately and "suddenly" aren't appropriate and I did not use them.
DD TTs using three phase motors. The new Technics, the SAT, VPI. I'm not sure about the NVS and the Monarch, but would be surprised if they weren't three phase, given their quality. Then of course there is the motor I build and install into my K3 design