If swordsmen are called "Katana Kachi" and spearmen "Yari Kachi", why are bowmen not "Yumi Kachi"? I would have opted for the English "pikeman", "longbow", "musketeer", but the names should be consistent.
Police and guard units carried swords because they were easy to wear in a scabbard and draw in the event of violence. A spear or musket is very unwieldy when not in battle. I doubt that these police and guards, mostly used to fighting criminals with lesser weapons (knives), would have been any use at all on the battlefield, unless they used surprise or the enemy were undisciplined in the art of the old cold steel.