It just inertia counteracts the speeding up of heavier objects because you have to put in more force to set them in motion (they have more resistance to starting the motion) so it balances out.
Haven’t tested it with skeletal meshes. Are the two in your video the exact same instances or can they have different internal parameters for parts of the mesh?
It seems the hanging ball rips off one of the meshes like the constraint breaks mid-flight