Lin Xin's team was the one of the best. They could easily defeat monsters of a lower level. However, their performance was rather poor during the fight with the Ursa Warrior, completely revealing their poor understanding of the monster's weakness and they lacked experience in engaging in a fight.
The Ursa Warrior's limbs were not equipped with armor. The ligaments in its knee were relatively soft. It would lose its ability to move if any part of the knee was attacked. Once its ligaments were injured, they could attack the femoral artery in its inner thigh. Basically, the Ursa Warrior would not be able to survive if its main artery was cut.
Of course, its eyes and mouth were obviously a weakness as well. However, Lin Xin did not understand it as she thought that she would just need to blind the monster. In fact, she could have just struck consecutive attacks on its eyes or shoot its mouth when it let out a growl. She could even hit its nostrils or earlobes.