There already are stat differences between different factions' line infantry, but they are quite subtle and have tried to be balanced for game play -never mind MP or not. Eg Austria's unit size is larger, but their drill stats are lower, i think Russia's line inf has higher moralle but also lower drill stats.

I did see, maybe on Heaven or TWC, a chart that someone had pulled together listing all the stat differences.

Maybe you aren't noticing the differences in game play or they are too subtle to be noticed? Changes to range would be pretty major, like the pre patch 3 double barreled musket debacle, and even in single player, totaly skew the game.