Yes. The worst defense of the Mendenhall era struggled...and it still finished 17 in rushing defense...and 14th in yards per attempt...
I kind of think you just pull stuff out of your hiney because winning and playing hard are two completely different things. They may not have won the way you liked...but there isn't much evidence to support them not playing hard.
As for the evidence of backs and receivers running through arm tackles. Just check Youtube. You will also see some phenomenal down field blocking by receivers...also a sign of playing tough, not soft. The best running offenses in BYU's history have been under Bronco. Your assertion simply fails and I award you no points.