Utah was invited to the Pac in June 2010. From 2006-2009 here's how BYU, Utah and TCU compared.
Overall record:
BYU 43-9
TCU 42-10
Utah 40-12
Top 25 finishes:
BYU 4
TCU 3
Utah 2
Record against each other:
BYU 5-3
Utah 4-4
TCU 3-5
MWC championships:
BYU 2
TCU 1
Utah 1
BCS bowls:
TCU 1
Utah 1
BYU 0
BYU was better on the field in virtually every single way compared to TCU and Utah in the period immediately prior to the conference expansion period yet we still weren't invited. It wasn't about on the field performance.