I believe synergy is the opposite of entropy and gravity does seem to be synergistic however such stratification (from less dense to more dense) is a localized phenomina and there are other forces. If such stratification continues a star is formed, energy is radiated, and most stars eventually explode but even carried to the extreme of a blackhole, mass is still lost to quantum evaporation.
Another example would be spontaneous crystal formation in a supersaturated solution but there would be the question of how the supersaturated solution was arrived at, kind of like the condensation of matter from the high energy of the "big bang".
The question in my mind is if our universe is a closed system or if the second law is a local approximation similar to an inertial frame of reference. A closed system would seem to preclude a "big bang" and where is the "dark energy" coming from?