Dude... overall's. don't. matter. At least when it comes to league-wide ratings. That's my tl;dr preface.
OVR's are reflective of the current users Player Type settings under Coaching Schemes. To my knowledge, every OVR you see for a player on your screen is based on YOUR settings for player type at said position. A 3-4 Pass Rush OLB's overall might reflect lower than his OVR would be if you run a base 4-3. Switch him to DE however, his overall will likely reflect closer to his 3-4 pass rush abilities. It just all depends on scheme settings and how a player's individual attributes account for those.
It's also seemingly been debunked in a recent thread about why league-wide sack totals start dropping off a cliff some 10 years into franchise, despite having many DL players in the high 90 OVR's... because generated rookie QB's
all enter the league with Ideal Pressure Sense traits. It's the traits and scheme settings that are slowly starting to materialize as the larger component to a player playing to the best of their ability based on the scheme the player is in.
This is why real life teams trade really good players for lesser compensation than what they would've requested had the player fit their scheme better, hence why Randy Moss was dealt so low to the Pats. His best days weren't behind him like the Raiders thought... he just didn't fit the speed-happy scheme Al Davis craved.
Madden's scheme system currently is nowhere near perfect, but it's at least getting better at reflecting RL NFL strategies the best they can. OVR's are no longer used as a final judgement on a player's ability and shouldn't be. It's an antiquated idea that should've been tossed out year's ago because there are so many variables to consider (see traits and schemes) besides a players OVR to decide if they work or not.