For me it's a tie between better luck with injuries and more explosiveness leading to more points scored on offense.
Believe it or not I felt even though lapses occurred the Defense played well overall. Even without yielding alot of turnovers they had their moments stopping teams when it mattered most minus the Bengals game.
I agree with you in general. The defense was 2nd in passing yards and top 10 in points allowed. If the defense needs to improve, it's with stopping the run but last year's defense was not the reason we missed the playoffs.
We have had terrible luck with injuries the past two seasons, and I think with even mediocre injury luck we make the playoffs the past two seasons (DEFINITELY in 2021, I think it's quite possible last year as well). And yeah, the offense needs more consistency across the board. O-line struggled, Dalton missed enough throws to remind you why he'd been bouncing around the league as a backup/spot starter, receivers dropped some balls, Kamara seemed ordinary, Ingram was clearly washed up. Each offensive weakness exacerbated the other weaknesses.