He used to. Then all the good defensive players retired or were traded. He's left with Vince Wilfork and a secondary that consists of swiss cheese, a failed cornerback turned safety, and some other practice squad quality players.
In all seriousness, I have to think it's the coaching at this point, they have the talent to be a middle of the pack defense, and indeed they're allowing points in that range, but man are they frustrating to watch.
I don't think it's the coaching, it's personnel.
Lets look at the linebackers, the only LB with any sort of range in coverage is Mayo. They go out this year and draft, what in my mind, is a two down backer. Spikes can't cover at all, good in the run game, can be an effective blitzer, good at headhunting. Bottom line, LB core is built to play in the 90's.
Days of the big physical linebackers are over, you need speed and guys who can cover, forget about size. Just a bad matchup against Gailey's offense, and he doesn't even have that many weapons on O outside of OL/Steve/Spiller/Fred.
A legit spread and shred offense, with multiple receiving threats and QB, will rip most NFL defenses apart. Guess it's why you see all the Chip Kelly talk. Don't even need the option, most of these LBs can't play in space. Most safeties are shit at scraping and filling, league is bereft of safety talent.