More durable devices don't mean "resist durability negation". The cut is durability negation. You can read in the first part where he cuts Or Gaule's dolls "like butter" and even cuts the mountain (which means yes just friction on air to cut the mountains).
Here are more dura neg cases i guess:
Anyway onto the points.
Casually, with ten meters of distance between them, he took up a stance with his enormous sword in his left hand resting on his shoulder. The instant she saw this manifestation, Shizuku's whole body shivered. There was no mistake. She could instinctively sense that this stance was for the 'One-Armed Swordsman' Wallenstein's true deadly technique.
Something is coming!
Shizuku immediately ended the rain of projectiles from Keppu San'u, and protected herself with the frozen mass of water. With permafrost that had an excellent protective strength, she formed a castle wall. With what should be called a stronghold, she had prepared a defense with perfect readiness—
"Shizuku—don't guard against that!"
In that moment.
"Bergschneiden."
Everything that protected her body was easily cut away.
If her judgment had been a moment late, her life would've been lost. At this truth, Shizuku gasped.
If Alice hadn't cried out, it really would've been dangerous.
An arm had been taken.
"Kuh…."
From the middle of the upper arm, her entire left arm had been cut away. From that perspective, the numbing pain crept up to her brain.
***
Wallenstein answered as he slowly walked up to Shizuku.
"Blocking, slashing, shooting. In this world, the effect of every type of power is greatly related to friction. No matter how fast the bullet, if its speed is stolen by friction at the point of impact, it would have no penetration and fall uselessly at its target's feet. And if an attack was altered by the same power, a blade can be made to unparalleled sharpness that cuts through any material without resistance."
A sword of excellent offense. A shield of divine defense. It was power that manipulated friction, which makes up the foundation of every kind of force.
"―That is the ability that I, the One-Armed Swordsman Wallenstein, possess."