The 49er's defense overachieved last season. This is great, but it saw a dip in production from one of the biggest names on the defense, Arik Armstead. So while you shouldn't focus too much on the numbers, there are still questions to be answered.
People want to focus on the sack numbers and forget everything else Armstead does well. Even I mentioned he could be moved inside with the already deep defensive tackle group. In reality, the Niners do not have an edge rusher consistent with Armstead against the run. Armstead has a case for the best run-defender on the team, although Nick Bosa is likely as consistent.