Su sighed for a reason. Those three bandits were indeed powerful, if they did not underestimate their enemy Su would not have been able to triumph so easily.
The three bandits had connected their armor and the metal-armored dragon into one entity in order to improve their coordination with the metal-armored dragon. This caused their actions to be restrained, they could not be as agile as a true grand swordmaster. Su managed to slice the bandits' throats accurately by releasing the Sword Aura in mid-air. He himself could not even understand how that happened.
If the enemy had transferred their Sword Aura into the armor and the areas of the armor below the mandible were made of magic beast skin, Su's Sword Aura could not have penetrated it. The effect would be akin to striking someone with a heavy hammer, the enemy would get dizzy.
Su had planned to cause a moment of giddiness in the enemy, he did not expect to kill them directly.
