In that stretch BYU finished ranked 4 times to Utah's 2.
BYU won 2 conference championships to Utah's 1.
BYU won 49 games. Utah won 47.
The head to head match up was 3-2 in favor of BYU.
Despite Utah having the best single season in this stretch, BYU was the better program in the 3 and 5 years prior to the expansion decision. Fortunately for Utah, the Pac-12 wasn't interested in adding the best program in Utah at that time. They were interested in adding a competent program that doesn't have the agenda that BYU has.