I do not see a undefeated team in the P% getting left out of the CFP unless there is one undefeated team from each of the 5 conferences, or that undefeated team played 2 FCS teams and a couple non P5' OCC.
I don't disagree with you necessarily, but I didn't think an undefeated P5 team would be moved down below 1-loss teams either. In week 14, the top 5 were Alabama (10-1), Oregon (10-1), FSU (11-0), MissSt (10-1), TCU (9-1). In week 15, the top 4 were Alabama (11-1), Oregon (11-1), TCU (10-1), and FSU (12-0). Like I said, I tend to agree with you, but they moved TCU ahead of FSU after they beat an unranked 6-5 Texas team. If MissSt had beat #19 Ole Miss to get to 11-1, I'm not sure that the committee wouldn't have put them ahead of FSU too, especially with all the love in the air for the SEC West at the time. The committee thought Alabama was the best team, even with its loss to Ole Miss. If Miss St, who played Bama to 5 pts, then beat Ole Miss, I could see them thinking that they're a top4 team. There was a lot of talk about wanting the best 4 teams and not just the best conference champions. I still think it would've been interesting. I suspect it would've still been the same 4, but I'm not as sure as you.