Just curious. Why do you think so?
It certainly wasn't very popular with most of its subjects. A very large diverse country weakly controlling immense fertile territories is a standing invitation to invasion by its neighbors.
AS I'm sure you know, in its heyday Poland was an unapologetically imperialistic nation. They even conquered Moscow several times.
Certainly, Poland-Lithuania didn't come up to present-day standards of liberty and democracy and self-determination, but no state back then did. It has to be judged more against other states existing at the same time, rather than against some modern standard.
And the options possible at the time also have to be considered: the break up of Poland-Lithuania did not mean that Ukrainians and other subject peoples got their own countries.
The idea that the old Commonwealth was or would have been freer than the Tsarist empire is also at least worthy of consideration. Arguably, too it served as a bridge between the West and the Orthodox lands, or if not a bridge, than a bulwark, something Westerners might well applaud.
I suspect the argument is similar to the great enthusiasm some people have for the Habsburg monarchy. I don't really share it but do sort of understand what's behind it.