This difference in density between the two objects might not affect the net holding them, but it will affect the way the objects interact with each other. For example, a clash between a diamond and a rock with the same mass. The rock won't be able to affect the diamond at all, while the diamond can tear the rock apart.
That is a simple way to explain the enhancement of quality brought about by Supreme Laws. But it is more complicated than that. Supreme Laws affect more than density and pressure.
For example, in terms of the interaction of laws, a concept of fire might beat a concept of water at the same power level because of its advantage of heat and energy over water. But a Supreme Law of Fire cannot beat a Supreme Law of Water. This is because, at that point, the Supreme Law of Water has lost its weakness to fire. It too can be hot and full of heat energy more than fire.
