The Lamanites were not easily defeated, even with these stratagems. These were probably trained Lamanite armies, with experience in hand to hand combat. Thus when they meet the Nephites they put up a great resistance. In addition to their probable fighting prowess, this is an army literally fighting for its life. It is aware that there is an army in front of them, and one at their rear. In such desperate straits, they fought doubly hard. It would have been apparent to them that the force in front of them would have been less formidable than the one at the rear, and that a breakthrough in this new front would still save their military objective. No wonder they fought fiercely.