I see your point, it seems like BYU would fit in well with a P5 conference.
But I think you need to look at the bigger picture. BYU's major sponsors, like Maverik and Grandma Sycamore's Fresh Bread, need BYU to be flexible. The restrictions and broadcasts involved with a P5 conference would ruin the relationship. BYU can't go tossing those relationships aside just to join a conference.
So, my friend, I'm afraid your post is wrong. BYU should not join the Big 12, because Grandma Sycamore's.