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.
Had the Commonwealth survived at least in some form, today it would have served as a powerful middle ground between the West and East and a lot of tragedies that went on to befall Europe could have been avoided.
Actually, P-L came pretty close. Very high personal, political and religious freedom. Very proud of it they were, too. They called it their "Golden Freedom."
Unfortunately, this freedom was solely for the szlachta, or nobility, who were perhaps 10% of the population. A major part of their "freedom" consisting of freedom to tyrannize over those who were not szlachta.
Much as in ancient Sparta or Rome, where being a citizen meant you could stomp all over those who weren't. Or the pre-war US South, where freedom and whiteness constituted a kind of rank in society.
The Golden Freedom of the szlachta of course meant they were also incapable of combining, even with each other, much less with their subject peoples, to resist subverson and/or invasion by better-organized, though less free, neighbors.