It seems some knights don't understand what their own weapons and armor do. Or at least, how the damage works.
Everything uses four (4) damage types in clockworks.
There is normal, piercing, elemental and shadow.
Normal damage comes from things like a Brandish.
Piercing damage comes from things like a Snarble Barb.
Elemental damage comes from things like a Freezing Vaporizer.
Shadow damage comes from things like a Nightblade.
The monsters in clockworks can resist some damage types and take more damage from other damage types.