The issue is that their schedule is so weak that if the other 14 teams in the top-15 played a similar schedule, I would guess at least half would come out undefeated.
This isn't a new system, G5 teams with weaker schedules know that they need to challenge themselves OOC if they want to get into the playoffs. But at the end of the day, UCF's best win may be over a 7-6 Pitt team -- who is a decent enough P5 team -- but shouldn't be the crown jewel in a CFP resume.
Schedule a ranked team or two out of conference and win those in your undefeated season then you have an argument.