I think you are right that BYU could have and should have taken the spot TCU took. To some degree, that is a blunder on BYU's part.
But you expressly request that nobody point out to you the clear statements from Holmoe and the B12 that indicate there really was never even a discussion about BYU to the Big 12. I have no problem blaming BYU for the result, but I can't ignore the best evidence about the process. And the best evidence about the process is that BYU wanted in to the Big12 and the Big12 wasn't interested in BYU.
I don't know why some fans want to believe that BYU spurned the Big12. I believe they are honestly confusing the stories and rumors about the Big East with those of the Big 12, to some degree. Based on Holmoe's frank comments, I can't believe that BYU was doing anything less than trying to get into the Big12. I guess he could be lying. Or maybe everyone reading the tea leaves and foregoing the things said by the actually people involved are not always correct.