The sword is (obviously) balanced in speed, attack power, and reach. Spears attack straight forward and can knock down enemies. Daggers have short reach and low strength, but allow Sword (the character, not the weapon) to attack quickly and use combos. The axe is the slowest, but most powerful class of weapons. It can hit multiple enemies simultaneously.
Really, in a game about dungeons whose landscapes periodically shift like slot machine reels, it's probably okay for a few things to be conventional.