4. Starting linebackers
At this point, I think it's safe to say everyone underestimated how big the losses of both TJ Edwards and Kyzir White would be in 2023 NFL free agency. The off-ball linebacker position often gets treated like the defensive version of the running back position when it comes to roster building, and teams can often find good players in the mid-late rounds.
Unfortunately, just like when you take a risk at the kicker position, you don't really notice how much better you used to have it until the replacement is out there causing problems.
The Philadelphia Eagles replaced both Edwards and White this past season with Zach Cunningham and Nicholas Morrow, having to make do without Nakobe Dean, a projected starter going into the season. Dean wasn't able to be on the field for even 200 snaps this past season, and while Cunningham did pretty well, Morrow was one of the worst-graded starters on the entire Eagles defense.
General manager Howie Roseman recognized that and wound up signing Shaquille Leonard as a free agent when the Colts surprisingly cut him during the season, but that only stopped the bleeding for so long.
I think we could see a complete cleaning of house at linebacker for the Eagles this offseason after the way this unit performed following some key departures.