The three metrics they are below 90th ranked are:
Yards gained per possession (94th)
Avg Kickoff return yards (99th)
Avg Punt return yards. (92nd)
In Yards allowed per possession BYU is 46th, allowing 27 yards per possession. (Alabama allows 22, Utah allows 25, Oregon State allows 41) I'd say BYU is not completely outclassed in the yards per possession in spite of their horrific bend but don't break scheme.
How about we blame the things they are bad at, for what they are bad at.