For Mormon, the Nephites’ military disadvantage would have highlighted their reliance on Yahweh for their salvation. Just as Mormon discounted the Nephites’ advantageous position above the Amlicites, here he emphasizes their disadvantageous position to underscore Yahweh’s help as the true source of their success.
Redaction: This verse, a summary of the day, is interestingly placed prior to Mormon’s description of the battle. His most crucial point is that Yahweh gave the victory, so he states it first in his narrative, then shows how it was true.