Vanras was an odd existence. This was what Ludwig came to realise after their first real exchange.
He was too heavy for his size, though it would seem he was incapable of flight.
But this didn't mean he was helpless from the ground. He can still fire crystal projectiles from the ground or even grow a spine at a rate which can completely destroy his armor if he got hit.
This was not a fight, it was a desperate attempt to escape this place.
When he came, the only thing in Ludwig's mind was success. He was not aware of the true plan nor did he know about any contingencies. Success or failure, these were his only options then.
And when Wilkis came, the answer seemed obvious to him. So he didn't fight back and chose to stop his struggle.
Being an Externalist, rationality was programmed into him through his experience. Fighting a war that won't bring him results is considered inefficient.