I'm still not convinced that Archers = Longarms, or vice versa. If that were true, than wouldn't it be less of a stretch to say Blademasters = Heavy Blades? Bows and Spears are just too different. Maybe the Archers in SIGN were just put there by accident, or to confuse us.
Heavyblades have stronger attack power, whereas blademasters are quicker. Heavyblades hold their swords with both hands and blademasters hold their swords with one hand.