While I initially found the P6 thing laughable too, from a marketing and psychology standpoint this may work over a period of years.

What really distinguishes the P5 from everyone else? Size of school? Amount of revenue? Attendance? TV viewers? Winning records? It seems an arbitrary and fuzzy line at best. No matter what criteria you pick, there are likely P5 schools today that don't measure up. There are also schools in the "G5" today such as UConn, Cincy, and BYU that were believed to be worthy of an invite to the Big 12. What the AAC is trying to claim here is that they are more like other P5 schools than the remainder of the G5 schools. From a mindshare perspective they seem "in between" the two today, not quite P5, but a step higher than many G5. I'm speaking mostly in terms of brand perception and pecking order for media deals, etc

Over time, if you see and hear something repeated enough times, it starts to become accepted as true. This is just the way humans are wired. From a marketing viewpoint, this may not so dumb, and it could eventually benefit the AAC. This is all about perception.