A Poland with sensible institutions wouldn’t have suffered from the dilemma of being stuck between Russia and Prussia; rather, Russia and Germany might have been at the mercy of Poland.
It was by no means necessary that the dominant state of north central Europe would be Prussia, or later a Prussia-centric Germany. Similarly, there’s no reason that the continent-spanning Russian Empire had to stop at the borders of Prussia, rather than a few hundred miles farther east. A Poland with more sensible institutions could have played an active role in structuring its institutions, rather than falling victim to circumstance.
That said, I haven’t the faintest real grasp of Polish history, can’t explain why Poland settled on the institutions it had, and can’t confirm that they had the impact that they’re reputed to have. Thus, this observation concerns only the structure of the argument, rather than its historical substance. Finally, I have no idea why people never mention the role of the Habsburg Empire in dissolving Poland; it would be better to say “stuck between Germany, Russia, and Austria.”