The fact is that it is seldom obvious. Unfortunately, it is left to the conclusion of sportswriters, most of whom have never played close to the level they are charged with judging. And most of those have a hard bias towards particular teams, coaches, and regions. Coaches polls are generally far more accurate, but hardly without bias.
But assuming that something in college football is "normally obvious" is a sheer fantasy, and especially when trying to discern which group of young men are deserving to be slotted where.