It's strange how you can go from having a top five defense and winning the SB one year, to dead last in defense the next.
I actually don't think they were the worst defense in the league though. They finished last in yards, but led the league in interceptions. Problem with that is if you don't get your INTs, you're screwed.
That is a mystery, but it does happen. After the Rams won the SB with Stafford, the whole team tanked the following year. Detroit got a lot of draft picks for Stafford, and those became high picks after the Rams tanked. I seem to recall at least one year where they had multiple, high first round picks.
And you're right about INTs. First of all they aren't predictable and second there's no guarantee they will result in points. Goff recently threw 5 INTs in one game and the Lions still won.
Anyway, back to the present, I like GB's defense. It's taken some time to adjust to Hafley and the 4-3 design, but they are now playing as well as anytime this season. We'll see how that works tonight against a loaded Lions' offense.