It is difficult to know how historically accurate Mormon’s description of the idle Lamanites in the wilderness might have been. Certainly, there could have been, but the descriptions of Lamanite culture we see during the mission of the sons of Mosiah to the Lamanites do not describe any such idleness. The Lamanites that the sons of Mosiah encountered were anything but idle, based on the clues we have in the text. However, it is also possible that, since it is Mormon providing this information, he is describing what he understands from perhaps six hundred years after the mission of the sons of Mosiah.
What Mormon describes is a time when there are not only Lamanites in the south, but also to the west and east of the Nephites. That description also appears to apply to later times. To this point in Nephite history, we have not seen evidence of Lamanites on the west and east. They seem to arrive through the pass near Manti on the south of Nephite lands.