Maybe the displacement sizes are not small enough. With more diversity in animated displacement, and rotation the instances should react on a smaller scale. But don't forget using a compute normal/compute terrain with a very small patch size in that case! Pop should sit on that compute node.
Though rotation will likely not be lineair, but more like haphazard rotation. I don't know how to get each instance to really rotate in different ways constantly. Then you probably need a few copies of a pop and have them rotate differently.
Mind you, I've never done this, purely theoretcal.