Oh no certainly not useless. Indeed the lack of infantry was one of the reasons the post 1700/GNW Polish army was bad. The infantry was just used different than  in 'Western' armies.

I think the main problem with the Polish Army/Infantry and wargaming it, is actually the political will of and in case of the GNW, lack of it, behind the army being on war footing. The commonwealth din't plan on entering the war (GNW), so the army as such was never properly mobilized. The different Nobles confederations that supported the Saxon or Swedish king, were I guess as a reult rather haphazard and adhoc compared to say the prepared and properly moblized force that arrived for the battle of Vienna.

It's interesting reading the polish version of the Battle of Kliszów for instance, where polsih Hussars easily smashed Swedish Cavalry, with only 12% of his force, only to get turned back b the Swedish infantry. The reason that the Poles retreat is in this case attributed to that Lubomirski decides that instead of comitting the rest of his troops to attack the swedish infantry, he orders the retreat as personal revenge against king Augustus.
How on earth do you wargame that solo! :)

Yes certainly the lack of will to fight and divisions within Polish society are key factors in explaining the performance of the forces in the GNW, and also the difficulty in recruiting enough infantry. These factors are difficult to reflect in a campaign but they are less of a problem on the tabletop I feel.

Despite unreliable Polish works on the performance of the army in the GNW it is clear that it was not to the same standard as they had been at Vienna. We reflect this by rating the units similarly to how they would be rated in the earlier period but we count them as 'Wavering'. This means that they are reluctant to commit fully and so suffer some handicaps in combat. But the main effect is that the Polish forces have low 'Army Morale'. Army morale is a reflection of how many loses the army (or a Wing or similar grouping) can suffer before it retires from the battle. 

A more balanced view of the Poles at Kliszow is that the they attacked but achieved little. Then for political/personal/other non military reasons the army withdrew from the battle. In gaming terms this means that the Poles fight as less effective versions of the army but with a low army morale. The low army morale is not because they are a 'bad army' but that they lack the will to fight at full effect.

This has worked in the GNW games we have played such as Kliszow which we did a few years ago - http://www.wfgamers.org.uk/resources/images/Gallery/GNW/KliszowSheffield.htm

And finally the whole battalion:

Fantastic :)