IMO, the faux narratives are
1. BYU's defense, overall, was really bad last year. They were very inconsistent and had some notable very bad lapses, but they also had a lot of good games. BYU held Gonzaga to their lowest offensive efficiency of the regular season last year. People only remember the bad games.
2. BYU is playing much better defense this year. Adjusted stats show that the improvement, relative to last year and relative to the rest of the nation this year that if there has been any improvement, it's been pretty modest.