Laman and Lemuel (and probably all of the brothers) are hesitant to face Laban and his fifty. As Nephi is exhorting his brothers to action, he calls to mind one of the greater fears, and then augments it through exaggeration. With the strength of the Lord, what does Laban's fifty matter? What would even tens of thousands matter. This last phrase is probably inserted for dramatic effect rather than any historical reference to Laban's ability to command that many men.