As said somewhere above, the function of the motor and platter is to rotate the record at a constant rate, inaudibly. Other "contributions" (e.g., resonance) from platter, motor, and plinth could be viewed as defects rather than assets so ideally should be zero. The same is true of turntable support. Once that is accomplished the rest is up to the tonearm and cartridge, correct compliance matching, and setup. And of course the condition of the record.
Breakdown of Turntable Performance
Over the years I've read numerous reviews of turntables, arms, platters, and plinths. I always wondered how much these individual components contributed to the overall sound. Here's my take:
Cartridge - 80%
Arm - 10%
Platter - 5%
Plinth - 5%
Cartridge - 80%
Arm - 10%
Platter - 5%
Plinth - 5%