Exactly. Slicing is dumb for armor. Armor's primary purpose is to defend against slicing and piercing (stabbing). This is why axes, hammers, maces, and to a lessor degree, spears, were all preferred against armored targets. Swords were a backup weapon or primarily used against unarmored targets. A back up to your sword is the dagger. The reason why it's long and slim is because it's designed to pierce through armor gaps, perhaps passing through ring mail, and still be long enough to create a lethal stab into something vital.