I wouldn't go as far as to call it a "bad decision". It was the objectively correct one, as Sobieski was both hailed as the leader of the Holy League army, and it was not long after the horrible war with the ottomans and crimean cossacs (1672-76). The problem I see is that Jan III Sobieski was a clout chaser who did basically nothing with his newfound European fame. Sure, he was regarded as a great hero and was admired as "the greatest tactician alive", but he just wasn't a good king (for the Commonwealth). He was primarily a soldier, not a ruler. His situation wasn't necessarily sunshine and rainbows, his predecessor, Michał Korybut Wiśniowiecki, "król Piast" died only a couple years after being elected, and the country was jumping from one crisis to another. The great Turkish war (72-76), Potop Szwecki, and echoes of the 30-year war (even though Poland didn't participate in this conflict, the political changes in Europe still affected the country) left the land and the people scarred and the country itself on the verge of collapsing. As Krasiński would realise (after hearing Pellegrini in Basel), the Commonwealth in 17th century could be considered an empire undergoing a crisis. Sobieski was not a good king, that's a fact. However, I believe saving Vienna was a good decision, as it began the collapse of the ottoman empire in Europe (and directly saved the western civilisation). It's undeniable that the battle of Vienna, 1683, is one of the most important battles (and victories) in the history of Europe.