I believe it's a combination of both.
The Packers having had success drafting offensive players doesn't automatically mean the defensive coordinators were the ones to blame for the unit struggling.
How many of the defensive players drafted in the first three rounds since 2012 (Nick Perry, Jerel Worthy, Casey Hayward, Datone Jones, Ha Ha Clinton-Dix, Khyri Thornton, Damarius Randall, Quinten Rollins, Kyler Fackrell, Josh Jones, Montravius Adams, Josh Jackson) have excelled playing for other teams???
There aren't a whole lot, meaning the Packers actually struggled to acquire talent on that side of the ball.
FYI the Packers ranked fifth in points scored in 2008 with Rodgers starting for the first time.
The Packers didn't have enough cap space to retain Rivera and Wahle in 2005. Thompson did a great job rebuilding the roster in a short time to make the Packers a contender only two years later.