I think musketeers firing system (fire by rank) works pretty slowly, so perhaps it would be time to improve it?
Im not sure if its possible, but why not make them "crossbowmen"=use "all fire" system! That way musketeers really would be important, know they are not very important.
EDIT: Another question:
Why people think Romans (true Romans, Byzantines) are overpowered? In high and late game they not special, im playing as France and i can easily take them down! Its only historical they got better start, after all, Roman empire existed already 1600 yers.. (or 1400, then it actually started getting stronger)