Before Zimmer joined the Bengals in 2008, Cincinnati's defense ranked 19th or worse (four times 27th or worse) every season that Marvin Lewis was the head coach. Zimmer joined the team and Cincinnati's defense never finished worse than 15th with two seasons ranked seventh or better...and the his D has finished in the top 10, 2 of the last 4 years.
Look at the Cincy depth chart? Not much there. None of them would start for us, yet look at his results.
Look at his division...