You put one chassis into plinths made of 4 different materials. I put 3 entirely different chassis' into plinths all made from the same material. The two experiments are not comparable. In response to your speculation about coloration, each of those three turntables has a characteristic coloration when auditioned in their respective stock plinths. In slate, they all became much more neutral sounding (which made them sound more alike but not exactly alike) AND the best qualities of those two drive systems (idler and direct) were not merely preserved but enhanced. That's all I can say.
So which plinth did you prefer? You did not say.
So which plinth did you prefer? You did not say.