Technically, the best offense is the one that scores the most points per possession, or times it has the basketball (so not on defense). Just cause we used 2015 earlier, we'll use it again. Wisconsin had the best PPP (points per possession, I just abbreviated it), but only had the 38th best defense (meaning, they gave up the least amount of points per possession, when they didn't have the basketball in the possession). Notre Dame had the second best offense, but the 102nd ranked defense.
According to these statistics, it isn't always true that the team with the best defense has the best offense as well.
My point is that in 2015, BYU had a great team on offense, but not a great team on defense. This is probably why we only finished third place in our conference.