This bit is not supposed to convey that everybody gathered together in the last battle:
11 And it came to pass that the army of Coriantumr did pitch their tents by the hill Ramah; and it was that same hill where my father Mormon did ahide up the records unto the Lord, which were sacred.
12 And it came to pass that they did gather together all the people upon all the face of the land, who had not been slain, save it was Ether.
13 And it came to pass that Ether did abehold all the doings of the people; and he beheld that the people who were for Coriantumr were gathered together to the army of Coriantumr; and the people who were for Shiz were gathered together to the army of Shiz.
14 Wherefore, they were for the space of four years gathering together the people, that they might get all who were upon the face of the land, and that they might receive all the strength which it was possible that they could receive.
15 And it came to pass that when they were all gathered together, every one to the army which he would, with their wives and their children—both men, women and children being armed with aweapons of war, having shields, and bbreastplates, and head-plates, and being clothed after the manner of war—they did march forth one against another to battle; and they fought all that day, and conquered not.
Anyone who could get that impression is a poor naïve apostate. That's the way it starts, just reading texts for what they mean, without listening to the whisperings of the Spirit.
Here is what we read in chapter 13:
20 And in the second year the word of the Lord came to Ether, that he should go and aprophesy unto bCoriantumr that, if he would repent, and all his household, the Lord would give unto him his kingdom and spare the people—
21 Otherwise they should be destroyed, and all his household save it were himself. And he should only live to see the fulfilling of the prophecies which had been spoken concerning aanother people receiving the land for their inheritance; and Coriantumr should receive a burial by them; and every soul should be destroyed save it were Coriantumr.
And at the end of the story we are told:
33 And the Lord spake unto Ether, and said unto him: Go forth. And he went forth, and beheld that the words of the Lord had all been fulfilled;
So we are told to expect complete destruction (apart from Coriantumr) by the word of the Lord; the process is narrated; then we are told that the word of the Lord had been fulfilled.
Survivors? Apart from Ether, only one apparently:
Omni 1: 21
21 And they gave an account of one aCoriantumr, and the slain of his people. And Coriantumr was discovered by the people of Zarahemla; and he dwelt with them for the space of nine moons.
Just as prophecied, no? If there were any survivors apart from Coriantumr and the prophet who brought him the word of the Lord, why then .. the poor old prophet got it wrong again!
by the way, this bit from the keyboard of Schryver is good:
For what it's worth, I entirely concur with your observation that the story would be LESS authentic if it met the expectations of these modern, extremist readers.
Of course the 'extremists' are not reading it in a modern light at all. They just want it to bear some vague resemblance to ancient warfare - in which nothing like this (with fighting children, for goodness sake!) ever happened. If it even bore some resemblance to decent fiction that would be preferable.
But it is just poorly constructed fantasy, such as one might expect from the half-educated. I wonder why?