Here are our records against the WAC/MWC opponents that we were in a conference with and how we have done against them since going independent.
1-0 Fresno State
2-0 Hawaii
1-0 Nevada-Las Vegas
1-0 San Diego State
2-1 San Jose State
That is 7-1 against them.
2-2 Boise State
1-1 Nevada
4-1 Utah State
That is 7-4 against the ones in the MWC that we were not also in the WAC/MWC with at any time.
That would be 14-5 (.736) against the current MWC. That is a better winning percentage than the .686 was against only the ones we'd been in conference with before. And the all time .661 (312-160) against all of the teams above.
Take a look at conference champs of the MWC since BYU left
3x SDSU (Co 2012 - lost to BYU 23-6; 2015; 2016)
2x BSU (Co 2012 - defeated BYU 7-6; 2014 - defeated BYU 55-30)
2x Fresno St (Co 2012; 2013)
1x TCU (2011 - defeated BYU 38-28)
Two times BYU played the team that lost the conference championship game as well...
2013 - USU lost to BYU 31-14
2014 - Fresno St
2015 - Air Force
2016 - Wyoming lost to BYU 24-21
W-L Opponent
24-7 Air Force
5-5 Fresno State
28-7 San Diego State
44-30 Wyoming
2-4 Boise State
47-35 Utah State
BYU has a .630 all time winning percentage against the top tier teams over the last 6 years in the MWC. They'd do alright in that conference. Especially when you consider that the last 6 conference champions (not named BYU) in their last 8 years in conference BYU only had a .371 winning percentage against. While in conference with those 2 teams that BYU struggled much more with than the teams in the current MWC BYU won 2 conference championships out of 8 seasons. They also placed second 2x and third 2x in those 8 seasons.