Mass isn't neccessary. Small, sharp slashing weapons can be just as dangerous- at least to the unarmored foe- as any other. A scalpel or razor to a major artery (femoral, carotid) will kill you quite quickly and effectively, especially in the hands of a trained combatant.
I once saw a trained knife fighter demonstrate a "carving" type counter strike to a blow from a right hand: this involved a block/grab followed by a shallow tracing up the arm, across the shoulder/neck, down the ribs and leg. It took less than 2 seconds. The resultant wound would have been very shallow, but because it crossed several major blood vessels, it probably have been fatal in minutes.
And as he also demonstrated, his knife was sharp enough to cut through a couple layers of clothing at that speed.
I once saw a trained knife fighter demonstrate a "carving" type counter strike to a blow from a right hand: this involved a block/grab followed by a shallow tracing up the arm, across the shoulder/neck, down the ribs and leg. It took less than 2 seconds. The resultant wound would have been very shallow, but because it crossed several major blood vessels, it probably have been fatal in minutes.
And as he also demonstrated, his knife was sharp enough to cut through a couple layers of clothing at that speed.