Lol... uhmmm No, they are not as good as Northern Illinois this year. Northern Illinois is on a completely different level every single season and they would compete for .500 or better consistently in the Big Ten.
Southern Miss is not Northern Illinois, not even close. As for McNeese State, Nebraska has played 15 teams better than McNeese State, since playing them. The lesson of McNeese State isn;t about talent or whether Southern Miss is better. The lesson of that game is showing up motivated and prepared to play.
That applies all over College football whether your're Auburn playign Jax State, Ark playing Toledo, Minnesota playing Kent State, or Missouri playing Ark State.
If Nebraska isn't mentally prepared, they definitely could get beat. But this isn't like playign Northern Illinois or another FBS program that will compete for 10 or 11 wins and easily dominate their league.