Ahhh, but you qualified the statement right there. Had we not gone to the CFP, the two best teams in those seasons wouldn't have won natties. And those two WERE the best teams...they validated it on the playoff field. The play on the field has proven the two high seeded teams didn't prove to be the better team when an actual game was played. Of the six years, only 2016 and 2019 had #1 and #2 win all the games.
But, I'll be the first to admit #1s and #2s have more total wins in the playoffs than #3s and #4s do. In fact, #3 seems to be sucking hind tit.
2015 #4 2 wins, #2 1 win
2016 #1 2 wins, #2 1 win
2017 #2 2 wins #1 1 win
2018 #4 2 wins #3 1 win
2019 #2 2 wins #1 1 win
2020 #1 2 wins #3 1 win
#1 seeds 6 wins (can add at least one more for this year w/ Bama's win)
#2 seeds 6 wins
#3 seeds 2 wins (can add at least one more for this year with Ohio State's win)
#4 seeds 4 wins