We both agree that BYU is not competing with the P5 champs and the highest G5 team for "a spot." BYU cannot take any of those teams' "spot." We all know that.
What you seem to be ignoring from my perspective is the subjectiveness of the ranking system and the concern for how far BYU can move up in such a subjective system. Generally it is not hard to think that subjectively the committee could move BYU up two spots. Moving up three and four spots in such a subjective system is just harder for a team that is not playing.
So, when we want BYU in the top 12 we are saying that is the goal only if the G5 and P5 champs are also already in the top 12.