I think the issue with the 4th quarter has been mental. You know these dudes can play! Also the type of defensive calls with a late lead too...that may be a MacDonald thing (though overall there's no disputing how much better we've gotten)
But you brought up a point I was about to make earlier: perception. I think the 4th quarter meltdowns have clouded things. What I see is a defense much improved from last year. Turnovers up, sacks up (an area that was supposed to be a weakness), secondary better. They just have to get out of their own way mentally late.