I think people WAY underestimate just how much of a black hole Tressel left for Meyer in the secondary and at LB. No, Tressel never had units as bad as the last two years have been, but here are ALL the DBs he recruited between 2008 and 2011:
Travis Howard (2008), C.J. Barnett (2009), Pitt Brown (2009), Dominic Clarke (2009), Jamie Wood (2009), Christian Bryant (2010), Jeremy Cash (2011), DerJuan Gambrell (2011), Doran Grant (2011), Ron Tanner (2011).
That's it, in 4 years. Pitt Brown was a huge bust, Clarke had a behavioral problem. Do you even remember Gambrell and Wood ever seeing play? Ron Tanner is the genius who got a 15 yard penalty on an egregious late hit on Saturday. He's seeing play for the first time as an RS JR, backing up a true SO. Orhian Johnson came in as a 3* ATH in 2008 ... and pretty much played like it. Four solid contributors in four (!) recruiting classes: Howard, Barnett, Bryant, and Grant. Same story at LB.
Meyer's entire tenure he's had 2 real stars in the D backfield (Roby, Shazier), 7 reliable-to-acceptable upperclassmen (Howard, Sabino, Klein, Bryant, Barnett, D. Grant, Orhian Johnson), 1 complete bust (Pitt Brown) and 1 near-complete bust (C. Grant), a bunch of Fr/RS Fr/So who were either huge liabilities or couldn't/didn't even play (Camren Williams, Perry, Perkins, Najee Murray, Powell, Bogard, Tanner, Reeves), and a bunch of guys whose name you would barely recognize. That's 9 acceptable players in two years for two units that have to field at least 7 players between them for every defensive snap. Almost any sub is a huge liability.
So when you complain that "Meyer arrives and D instantly takes a nosedive", please remember that it takes years to develop players and that everything Meyer has had to work with came from Tressel.