Your reaction is quick, but hidden dangers are harder to guard against.
Sianweistan is not a panacea. After learning from a previous loss to this type of prosthetic with the Tiger Claw Gang, Lin Miao has become especially cautious. He doesn't want to end up failing in an unexpected situation, having his chicken stolen by someone using Sianweistan.
So even though the front line was in the heat of battle, he only fired from the second floor, hidden.
When Tariq finally couldn't hold back and charged out, the battle came to an end.
The death of the commander and overseer made the morale that the Night Wanderers had just mustered crumble completely. Without anyone holding them back, they started fleeing in their vehicles one after another. The shift from disadvantage to rout was almost instantaneous.
It's no wonder they were so fearful. Have you seen anyone dare to stick their head out under machine gun fire to shoot back at you?