Dgad, suspension in cars and isolation from periphery vibrating ground (shelves, floor, wall) has very little to do with each other.
While your thoughts do indeed reflect some popular high-end audio "theories", they are not on a solid physical basis and are not hitting the topic.
In resonance frequency and the isolation from parasite vibration "we" are - should..... - seek a resonance frequency below 1 Hz.
Check the website of Minus-K and other companies dealing and specializing in this to get some insight into this topic.
3 motors will introduce - as they can hardly be synchrozised - 3 sources of error into a rotating system.
To this just add the belts which do elastically speed up and slow down - i.e. introducing wow and flutter - the platter and you have a rotating system which is the very opposite of constant unaltered speed.
You don't hear that the TT sounds worse with multiple motors?
Most likely because the bearing is now force free if the motors are situated in a manner that the bearing is horizontal free of force or close to that.
As this will "better" the sound, most will credit this improvement to the multiple motor situation.
However - using only 1 motor and 2 counter-bearings in the positions of the other "motors" instead will further improve the sonic presentation.
Multiple motors is the very same conceptional error as with multi-tubes or multi-transistors output-stages. As the individual tube/transistor/motor is always NOT identical in all parameters to its "comrades" the resulting "signal" is itself not homogenous but "wobbling".
This is something to think about before telling me how wrong I am.
It has to do with strict logic and theoretical model without prejudice.
We should have some members here who do enjoy exactly these ...........