Even though Mormon and Moroni saw the story of the Jaredites as a type of the destruction of the Nephites, there were significant differences. One of those was ultimogeniture, and the other is the fascinating Jaredite practice of capturing opposing kings and keeping them in captivity. That happens again in these verses. Coriantumr is defeated and brought into captivity, and then his sons are able to free him. It is a pattern often seen in Jaredite history.