It seems that in the late 1700s (post Partition) and throughout the 1800s the restoration of Polish independence was a major liberal/revolutionary goal, and that Polish officers serving in foreign regiments were seen as romantic/heroic figures for liberty. Why was this the case? To my limited understanding of the subject, Polish nobles had many rights, but their serfs were poorly treated--hardly a good sign for liberty.
It sounds like a rueful comment on the failure to adopt a stronger Constitution until it was too late - in particular, any member of the legislative Sejm could until 1791 veto the decisions of a whole session, nullifying an estimated third of its deliberations. I suspect the "liberty" said to have "martyred" the Commonwealth was precisely that of the nobles who had fought tooth and nail against a strong monarchy that might preserve the realm but would erode their power, whereas the concept that inspired later revolutionaries and romantics was indeed more national.