The final measurement of the 2018 Alabama football secondary came in a national championship failure. That measurement is not completely fair. An impotent pass rush made the secondary vulnerable against Clemson.
At least one player, Josh Jobe, was thrust into a pressure situation in which his playing experience was inadequate. Consider all the above and the results were predictable.
Results should be very different in 2019 (and early 2020) for several reasons. The primary reason is the difference in playing experience going into 2019. At the start of the 2018 season, Alabama football returned three members of the secondary with starting experience.