That's debateable about whether a G5 school should have a seat at the table. If you don't allow them a chance, then let's call it the P4 tournament + 1 independent (ND). Here's a differing perspective
https://sports.yahoo.com/college-football/article/jmu-tulane-and-other-g5-schools-belong-in-cfp-no-matter-what-espn-says-180654232.html
The formula allows 1 G5 school to be selected amongst the number of non-P4 conferences. The ACC did it to themselves with their own formula allowed a 5 loss team to play for the conference championship. Had Miami played, they would have either been in as conference champs or would have been eliminated most likely with another loss. If Miami wins, they are an automatic qualifier, and knocks out a G5 school. (would have had their normal 1 in the playoffs) and ND has a slot. Conversely if Miami plays and loses, most likely they finish behind ND and ND is in. So the ACC has to own their process.
As does ND...they not only elect to not be in a conference, but to be "half in-half out" of the ACC for football. They play 5 games in the ACC, and it just happened that the ACC was down this year. ND beat up on a bunch of bottom dwellers. So their overall SOS was poor, and they lost their 2 biggest games, including Miami which put them on the wrong side of the tie breaker. ND wins one of those 2 games, they are in.
So ND has to own their destiny and be accountable as well. They win, they are in. They join a conference and are successful, they are in. (especially one of the stronger P4's) They didn't do either, so they have to look in the mirror as well. A 16 team tournament would eliminate this from happening, but ND needs to challenge themselves with conference membership and or playing a tougher schedule. ND wants their cake and to eat it too....they want their own TV Network and not into sharing revenue. OK...but that comes with risk. This time, things didn't go their way.
Blame the selection process, blame the ACC process...but ND has to take a long look at themselves. They are not complete victims.
BTW before I get labeled as a ND hater, the Irish are my second favorite college football program. I wish they were in as well.