Responses

I don't think it was about his skills as a martial artist but about his character. He was introduced as a great leader trusted by his troops and as an incorruptible person (as he risked his life to send an anonymous letter for the army's corruption).
Plus if he had his own troops to begin with that means he's pretty strong, he wouldn't have been chosen as an officer if he was weaker than his own men
Was jang ho really that great?? Wasn't he just avg martial artist? Anyways good for mc he seems to be the type who's super loyal