So, what was their offenses rated?
And, were teams that were imbalanced, a real highly ranked defense with a lower ranked offense, and vice versa, how did those teams fare?
As time goes by, the defensive stats lost their weight,while offensive stats gain in theirs.
Now, since the advent of the rule changes, there are several exceptions,as you noted, but go back further, where many draw their conceptions of how defenses should perform, and those exceptions dry up.
It doesn't matter, Oklahoma 3 times and Oregon are a combined 1-4 in CFP games. They are the epitome of high powered offense and no defense. They won the games against the teams they scheduled in the non-con and won the games against the teams they were most familiar with, then when they played teams with better defenses, they lost. Alabama had the 6th rated offense in 2018, they scored 16 points against Clemson. Notre Dame had the 32nd rated offense in 2018, they scored 3 points.
I have said multiple times that the offenses are better and that what is considered an elite defense today with regards to yards allowed, points allowed and yards per play, probably wouldn't have been considered an elite defense in 2001, but the fact remains, that the team with the better defense is winning the games in the CFP to the tune of 73%.
When Clemson and Alabama played, their offenses were ranked 3rd and 6th respectively. Final score 44-16 Clemson.
Going back to 2009, the rankings in total defense are as follows:
Alabama - #2
Auburn - #60
Alabama - #1
Alabama - #1
Florida St - #3
The exception was Auburn who beat Oregon in the championship game, Oregon had the #1 offense in the country that year, and was only able to score 19 points in the title game. Oregon had the 34th best defense that year. Probably the best ranking they had over the last 10 years.
So in the last 10 seasons, in the BCS title game then the CFP semis and finals, 15 out of 20 games, the team with the better defense wins. I don't know about you but 75% is a pretty decent number.
Also note that in 1 of those 5 losses, Clemson in 2016 had the 8th rated defense in the country.
When it comes down to winning a title, outscoring a top 4 team 2 weeks in a row is going to be difficult. As Oklahoma and Oregon have proven 4 times in the last 5 years.