BYU gets beat up when they play P5 teams week in, week out. BYU beats Toledo 99% of the time if they don't have Washington, USC, Utah, Tennessee the four weeks leading up to that game. 

Going MWC allows BYU to schedule 3 tough P5 schools, then a FCS school, then conference play. You start out 1-2 or 2-1 every year, like BYU did in the MWC. Then BYU gets a FCS team. BYU heads into conference play 3-1 or 2-2 with a shot to win out. If BYU does, they finish with 10+ wins, ranked and a shot at a NY6 Bowl game. 

Life is good. BYU gets into conversations about playoff worthiness, even though they will never make the playoffs (but BYU will never make the playoffs now anyways, so it is a moot point). BYU gets to have a big showdown on tv and the whole world watches every bowl season vs a PAC-12 team or a P5 school in a NY6 Bowl. 

It is what BYU was made for. 

In the PAC-12 Utah is a second tier team. Anytime USC wants to beat Utah, they can (see two games ago). When Whitt leaves who knows what Utah will be. They have potential to be UW. They also have potential to be OSU. In my lifetime, Utah will miss bowl games and have 3 win seasons. 

In the MWC/ACC, BYU should win 10+ games forever. BYU would be the perfect stepping stone job. Come in, win a lot of games, move on. BYU could be Houston. Heck, Houston has a very good P5 coach as their HC. BYU had that with Bronco. And could have it again. 

BYU may never reach the mountain top again, but odds are BYU never will anyways. So, instead of aiming for the peak that is unobtainable, getting to the second or third highest peak consistently is pretty awesome.