I believe you are right.  Utah went through this in the early stages of being in the PAC 12.  It competed most of the time, but if a starter went down, or worse, 2 or 3 starters, it became a rough road to haul.  What separated Washington, Stanford, and USC from Utah was they lost starters all the time, but nobody really noticed.  The other major benefit of having strong 2s and 3s is that is who the 1s practice against all year, and for some of them, for 2 or 3 years.

For example, I knew Utah's OL would be challenged by BYU's DL, but I had confidence that they would compete and maybe even do well because look at who they practice against every single day.  Anae, Tupai, Tafua, Fotu, and Penisini are a handfull. 

BYU will improve when the 1s can play better competition vs the 2s.  I have friends who played for BYU.  They told me during camp that Zach was ripping apart the secondary and that Williams looked great.  That is a bigger concern for me that it is a motivator.

Utah reported all summer that at times the offense won camp that day, other days the defense one.  A balanced team of good 2s and 3s will create that practice environment.