If we take Bama as the example, they sped up their offense last year all the way to the 72nd fastest pace in football. Blazing, I tell ya. Anyway, it resulted in their ceding 1 minute of TOP to the other team. 1 whole minute. That's 3 whole plays even for the fastest of teams. His defense is really worn out by 3 more plays?
Speeding up his own offense had nothing to do with his opponents running significantly more plays against his D. Opposing offenses speeding up their own tempo is what is causing his D to have to run more plays. There's nothing he can do to stop that other than whine and hope other coaches take sympathy on his poor defense.
Now BYU, otoh, has ceded roughly 3 minutes TOP to the other team since going to GFGH. That's 9+ extra plays a game. Now, if we're Oregon and scoring on half our drives, we wouldn't care. Who cares if you're giving the ball right back after another TD? The other team can't keep up, anyway. But our offense hasn't gotten there yet, so holding onto the ball a little longer probably would help us out some.