Ha! I enjoyed this! It's like shutting Philip Glass and John Cage into the same room and having them duel each other on pianos (of course you'd have to take out the black keys before allowing Cage to his piano. And take away any screws and rubber he might have in his pockets, or he'll put them between the strings)
Nice concept too: a very simple and straightforward answer to the ever-present question of variety vs. unity, by totally isolating those two elements on two different instruments and exposing them at their extreme forms: Quasi-free improvisation and a simple repeated motive. And simple answers are good, if they work, which they do here.
Contrary to pliorius I never wished for the first piano to be louder. I mean, after all you know this motive after a while, so all you need to know as a listener is that "it's still there". It might become annoying with time if it was too strong (which might also be a compositorial goal of course).
Did you have any spacial placement in mind for this? Like positioning the two pianos at different places in a room? I think that might even add to the concept of separating the two musical elements of chance/expression/variety and order/structure/uniformity.