Engineering is all about compromise. They look at all the equations and variables, determine the consequences, good and bad, of each feature of a design, then decide which features are most important based on the criteria they are given for the finished product.
A rear tire may have more tread, but there must be SOME trade-off to give the front tire less tread. Car tires may perform very well, but there must be some trade-off for a motorcycle tire that makes them stick with it. We may not understand the reasoning for the engineers' calls, and the reasoning may not apply to our uses, but it was done for a reason. We may be able to adapt their designs, as in reversing the rear tire when used on the front, but we should ask ourselves why. What was the trade-off for their original design and what are we accomplishing by modifying it?
Not saying the modifications shouldn't be made, just saying they should be thought out and have a purpose and ALL trade-offs of each modification should be considered.
In answer to the OP, my understanding is that the rear tire pushes while the front tire is pushed. Therefore, assuming the tread pattern influences leverage and application of force on the wheel, the tread pattern should be opposite from front to rear.
Water dissipation, while a serious consideration in tire design, is not the primary factor. For big, off-road tires, you want a thick, deep tread pattern to provide "hooks" to grab the surface you're driving on. For racing, slicks provide far more contact with the ground, providing better traction, but don't provide the proper friction coefficient until they reach a certain temperature. Because the speed must be so great to obtain this temperature, it's not practical for a road car. Racing and off-road, by the way, have predictable surface conditions. Regular daily driving does not. Therefore, there must be a compromise to account for the unknown.
My question is, why are we even still at the stage where we have to discuss tires? I thought we were supposed to have flying cars by now dang it! Hollywood lied to me!