The FBS playoff is the only postseason where all the participants are elite, and where all teams that make the postseason were great from start to finish. FBS is the only sport that encourages greatness every week.
There is no resting starters for the playoffs. There is no load management in FBS college football. There is no debate on whether or not you should try to go undefeated or have the best record in history because you might get hurt or be too tired for the playoffs.
The flaw with FBS isn't the postseason. It is that there are too many teams in FBS. FBS should be only 32-48 teams as they are the only ones that have the ability to compete at the highest levels of college football. The bottom 1/2 to 1/3 of P5, G5s, and the top FCS teams should form a new division and have an extended playoff.