Seems to me this conversation is getting a bit strange. Someone is saying the mechanical amplitude of cantilever movements should be the same for different carts, or types of carts?
That's a bizarre notion. Maybe you're looking at the stylus end of the stick? What really counts is the generator end. That's where the cantilever delivers the goods - excites the generator and converts mechanical movement to electricity.
Compliance is a measure of springiness. Would you expect 2 cantilevers with different springiness, made of different material, and of different lengths, to vibrate/resonate and deflect the same?
I think the reason you can get decent results with a 64S, is because the arm/cart resonant frequency with a 'normal' cu cart goes down rather than up. If you have a stable platform you can tune the combo with compatible headshell, tonearm wrap, damping, etc. and whatever works as long as it tracks and your woofers aren't jumping out of their baskets.
If you use a low cu cart on light arm, the resonant frequency goes up and approaches or enters the audible band which results in intermodulation distortion. IMD can sound euphonic here, reinforcing the bass or midbass, although it can cause involvement many octaves above the resonant frequency.