Last year was a shocker for me but I think Rex gets too much of the blame.
Most statistics had us as a middle of the pack defense (not the worst in the league as you would think). Obviously well below expectations, and the previous year. Rex was not the only variable. Major injuries (Kyle & Aaron we're two big ones) without proven depth behind them at the time, an aging malcontent in decline- :"traffic cone," and a complex new system in year one of the install. I think we should have brought in a couple veterans last year to help install (David Harris), our young defensive core just didn't seem to get it (Preston Brown). Looks to me they get in now and we've brought in some great Dline depth and secondary talent.
I'm chalking up last year to the learning curve.