While thirty thousand is a round number (and hence possibly representing idealized troop units), it is still a plausible figure for the Nephite army. (See Helaman, Part 1: Context, Chapter 4, “The Meaning of Numbers: Counts and Estimates in the Book of Mormon.”) In fact, it may be Zarahemla’s regional army, since this battle apparently did not involve communities farther down the Sidon.
After the Nephite victory, the Lamanites retreat and four years of peace follow. Although Mormon provides some detail, his treatment is more parsimonious than the battle accounts in Alma before the Savior’s birth. He chronicles multiple battles but without details of tactics or officers. Mormon’s purpose is obviously to chronicle the Nephites’ demise. Furthermore, he probably did not find personalities as admirable as Captain Moroni.