> Now, you may be thinking "but shouldn't the bits of planet-fluid under stronger gravity sink and push on the fluid around them and thus indirectly cause stuff to move around to the sides?"

that was what I was thinking.

So the reason we see gradients is because areas that are experiencing low force have lots of mass, and areas experiencing high force have little mass.

Looking at the diagrams, I guess I can see that is the case.

Thanks for clearing that up!