In the last 8 years, even BYU's best teams have had some blow-out losses to teams like:

• FSU and TCU (2009, 2010)
• Utah (2011)
• Oregon State (2012)

They also have a losing record against Pac-12 teams over that span (7-13 against Pac-12 teams since 2009). 

I know that BYU would get some sort of a recruiting boost for P5 affiliation, so they probably field some better teams over that span (and maybe they keep Bronco). But even then, I don't see BYU being a better team than:

• UCLA in 2011 (the year that Utah beat BYU 54-10)
• #17 UCLA in 2012 (8-5 BYU team that lost to Oregon State)
• #11 ASU in 2013 (8-5 BYU team that lost to UVA and a UW team w/out a coach)
• #8 Arizona in 2014 (8-5 BYU team with losses to Utah State, UCF, and Nevada)
• #24 USC in 2015 (9-4 BYU team that lost to UCLA, couldn't move the ball at Michigan)
• #9 Colorado in 2016 (9-4 BYU team that lost to UCLA and Utah)
• #11 USC in 2017 (4-9 BYU; worst team in our lifetimes)
• #17 Utah in 2018 (So close, but no cigar – and BYU's lead shocked us all)