Continuity mistake: When Mulan is being rescued during the avalanche, they shoot an arrow and Yau grabs the arrow with the point down. The next shot, he is holding the pointed end.
Continuity mistake: During the fight caused by Mulan when she first arrives to the camp, Ling gets several of his teeth knocked out. But the next day, his teeth are all back in his mouth.
Continuity mistake: In the scene after Shang became a captain, Shang says "Soldiers" there is an underneath shot of him, and there is no gray stripe on his pants but then the stripe is back in the next shot.
Answer: For the reasons stated. He believes him to be a highly competent soldier and trainer. While this opinion is probably influenced by Li Shang being his son, it does prove to be correct, as Li Shang's training is what allows the small group to succeed in battling the Huns.