Another one is that Poland had an unusually large proportion of nobility in population by Europe's standards, especially of that time. So who's gonna be the cavalry (and providing a big chunk of its expensive gear plus a decent rider to use it) in such a cavalry heavy army?
Becouse when in theory our gentry had common people in disdain,in practice in military they hired anybody who was competent.
Winged hussars,for example, was semi-private unit,when one gentry buyed horses and armour for himself,2 others who usually were gentry but could be able commoners,2 wagons and about 15 armed commoner servants which could be used as infrantry or light calvary.
Polish state gave him money,but it never covered more then half of expanses.
In medium and heavy calvary soldiers were almost always gentry,but light calvary and dragoons were mostly commoners.
About coping - winged hussarls would go throught any infrantry,and
And about our gentry levies - career gentry soldier have them in real disdain and prefered able commonners.
So,as long as it remain fighting force,commoners were there ,althought they never could made career bigger then dragoon or light calvary commander.
About what
@Buba said -
1.yes, they horses in good condition,but they could made circles near any western army without making horses weak.
2.In 1792 our cowardly king surrender when he still have army and russians crossed Bug river - but with Sobieski style 10.000 strong calvary corps,they would be beaten few times before that,so he would continue fighting.
Poland would win 1792 war,and strong Poland would change everything in History from that point.
3.Our armies have winged hussarls who break any infrantry and calvary in open field,medium calvary which break any calvary and most infrantry,and light which always blind enemy scouts and found him before he found us.Dragoons would hold terrain.
So,coping it for part of other army/no more then 10.000 need/ would basically destroy any smaller enemy army,and let you attack without knowing where your army is.