This must have been discussed in the past, but what's wrong with them? At least one of their Generals (especially one that spawns later) should be a 3-star General so they can create an army. Otherwise the CP penalties are so high they are almost useless unless the gamey "solution" of bringing an Austrian or French or Russian 3-star General to command them.
I know that in real life they were hindered in their command abilities, which is something the devs try to portray in game, but the Swedes become a liability after a while. In our MP game they have contributed to my abysmal low NM by the series of defeats they have suffered. I have tried as a maniac to retreat them, move them out of the way, undercommanded (35% penalty), undersupplied, battered. It is such a frustration.
I believe at least one of their Generals (the substitute that comes in 1757 for example) should be a 3-star so they can be effectively commanded. If you need to lower their numbers for balancing reasons it might be better than this. The inability to create an army/corps structure with them is a show stopper.