There QB, top RB, and top tackler all return. While they were down last year at 7-6, they averaged 10-3 the prior three seasons.
They also beat Boise in Boise last year (where BYU could not).
BYU has also struggled against G5 bowl teams the last three years (2-7 regular season, 0-4 on the road) so it's not like BYU is killing it against these types of teams.
I put Toledo, USF, and SDSU all in the games I really expect/want BYU to win but wouldn't be surprised if the Cougars lost.