exactly, but the gp threw in the caveat

gp> then galaxies are not moving in the way we currently think they are.

so if our calculations already take into account the gyroscopic movement of the bodies within the system, still the gp's thought experiment accounted for this by saying the real nature of the motion of the bodies is different than the motion that we are currently using in our calculations

just saying dark matter ignores the potential for other valid explanation for the phenomena

instead of there being dm offsetting the center of mass the gyroscopic motion of the bodies within the system also could explain the offset

'not moving in the way we currently think' is a vague statement and could be a direction of rigor for the gp if thae wished to pursue the idea

some underlying questions that need to be answered by anyone that suggests our current understanding is incorrect in this regard would need to address:

    how are they moving differently? 
    how could we detect the difference?  
    how can our incorrect perception be explained?

my> the movement of gyroscopes can alter a system's center of mass

the cube video was intended to show that yes, this is well understood, and exhibit how changing the nature of the rotation of the gyros: location, direction, speed; in the cube you could move the center of mass to wherever you'd like

add another dimension allowing the gyros to move freely stead being fixed within a cube and even more freedom to alter the center of mass could be achieved

https://www.youtube.com/watch?v=UnpLEnIqj_A

i agree it is well understood.. that is why i was using it as naive evidence to defend the gp's thought experiment from being dismissed poorly