An ideal liquid has uniform pressure. Water is not an ideal liquid.
Water does compress. We just mostly ignore it because it doesn't compress enough to matter most of the time. A kilometer deep, water molecules are a tiny bit closer together than closer to the surface, and given that the force between the molecules is inversely proportional to the square of distance, a tiny difference in density can mean a huge difference in pressure.
You're considering water molecules randomly impacting the steel ball. But that's really more how gases work, not liquids. Liquids are condensed matter, just like solids - intermolecular forces are what prevents their compression, not statistics. The molecules that hit the steel ball don't bounce away into oblivion, they bounce away from the other water molecules and back to the steel ball, moving (mostly) back and forth. In a simplified scenario, you can assume that while the individual molecules wiggle around, they don't really move freely as in a gas. Each molecule interacts with the molecules around itself, unlike in an ideal gas as long as the liquid is static enough (e.g. uniform temperature, no currents etc.). Liquids don't obey the ideal gas law, obviously - the relationship between pressure and density is not linear. Which is a good thing, really, otherwise we wouldn't be able to walk :P
If you want a more realistic depiction of your scenario, consider that there's a tiny bit more molecules around the sphere as you increase pressure, because the mean distance between the molecules is a tiny bit shorter, and the the forces between the molecules are much higher, which also means more push of the water molecules against the steel ball; the water molecules get closer to the ball on average, so the force between the average water molecule and the average steel "molecule" (I'm going to go to physics hell for this, aren't I? :P) is higher. Since the intermolecular forces are very strong in a liquid, a tiny change in density corresponds to a very large change in the forces involved, and thus pressure. Don't forget that ultimately, the pressure comes from the electromagnetic interactions between the individual molecules, whose strength is inversely proportional to the square of distance. The water at the bottom of the Mariana trench is cold because it is denser than the warm water at the surface - otherwise, it would rise in a convective column and be replaced with less dense water. Liquids aren't ideal gases.
You might also want to consider a closed container entirely filled with a liquid with no surface. There, you can easily see that the pressure is equalised - that's the whole mechanism that makes hydraulics work. Of course, different liquids have different compressibility. This only works when the pressure is high enough to make the differences in the other forces (like gravity) insignificant - the deeper the container, the more pressure you need. To have the oceans behave this way, you would need to apply as much pressure from the top as is on the bottom, which would be quite the endeavour :P Even if you just built a hydraulic column that's a kilometer tall, you'd need to apply a pressure of about 27 MPa (for ocean water) before it started behaving "nicely" - that's 2700 tonnes per square meter, about three times as much as the ground-level atmospheric pressure on Venus.