It is said that at small sizes, icy planets are more likely to be in hydrostatic equilibrium than terrestrial rocky ones. But why, as a matter of fact? Shouldn't denser bodies be more likely to collapse into equilibrium (I'm talking of equilibrium achieved by self-gravity only) and be more able to remain in that state?
Hydrostatic equilibrium for celestial bodies occurs when the internal gravitational forces overcome the rigidity of the materials of the body.
So, a dense rigid body may not be in hydrostatic equilibrium, while a similarly-sized, less-dense, fluid body could be in hydrostatic equilibrium.
Similarly, while rock is more dense than ice, it is also more rigid. So one can't assume that the minimum radius for hydrostatic equilibrium for a rocky planet is necessarily less than the minimum radius for hydrostatic equilibrium for an icy planet. I don't know if such radii have been conclusively determined for various compositions of bodies.