This is my assumption, so that first read is the #1 receiver with the 6 step speed out right but usually the slot which is #2 receiver is running a vertical deep route which takes longer to develop and clears space up for the mesh. The #3 receiver on trips and the lone receiver on the other side mesh which is a faster developing route than the #2 receiver going deep. So it goes, 1st read speed out, 2nd read mesh coming from backside, and 3rd read #2 receiver route.
Not sure how people put coaches down. As if you can do what they do. If you are reading this theres almost a 100% chance the worst coach at Oklahoma is better than you will ever be. Just watch the damn games and shut the hell up