Actually, in vanilla M2TW gunpowder troops are less effective at killing the enemy than advanced archers/crossbowmen. In a head to head pitch English longbowmen would absolutely decimate aquabusiers. Likewise Aventurier will beat musketeers. Furthermore like Cute wolf said archers/crossbowmen are also much more able to hold their ground in melee. The only real advantage gunpowder units have is that they cause fear factor among the enemey. I only use musketeers because they look cooler and are historically accurate. Elite archers and crossbowmen are much better, not to mention that gunpowder troops can't shoot over head, which would be a problem at times.