I would just look to the first half of the season when Rams had their stars playing.
When you remove Stafford and Donald on both sides of the ball.. then I would say it is bit unfair to judge the offense/defense during that time.
So in the first half or so... Rams Defensive rankings were in the top quartile I believe... definitely top half.
If we look back to those games, the defense kept the team in the game for 3 quarters, while the offense struggled.
Even when we had the lead, the offense could not generate extended drives in the 4th quarter. So many 3 and outs.
At a high level, the issue I saw was the lack of recognition that the Offense was going to continue to struggle.
Seemed like the staff thought they could get the offense going, so the defense remained in their normal scheme which is built to limit big plays and let the team play catchup while the offense scores TDs. It's like.. trust us, we'll start scoring TDs, so keep the defensive scheme as is.
I don't think it was more of the defensive staff's fault at this. But more of McVay. After Stafford went out, then there seemed to be a realization that the offense wasn't going to get going.... so we started to see a shift in defensive philosophy. But by then, it's too late.... it's half way through, not enough time to install completely new things and then key players started to go down like Donald.