Not solely schematic. There was a talent issue too.
Kris Boyd was super talented, but had poor discipline. Holton Hill was more undisciplined off the field than on it.
Deshon Elliott left after the 2017 season, and that was a pretty good defense that year.
Brandon Jones had great athleticism and run support, but bad ball skills.
Chris Brown was limited athletically, but solid in run support. BJ Foster got worse every year after his first, overall lack of discipline. DMo is a linebacker.
PJ Locke was solid and a likely victim of a bad scheme.
D'Shawn Jamison could also have been used better. I think Josh Thompson has all the talent in the world, but he was just always a step or two late.
Sterns was hurt often after his great freshman season, and tried to play through some injuries that made it tough for him to make the same plays we came to expect.
Most of the guys they recruited at DB were overrated. Jalen Green lacked the speed and technique to play corner. He finished as an average safety at Miss St. Chris Adimora finished his career as a linebacker at SMU. Kenyatta Watson, Tyler Owens, Xavian Alford, etc.