He's a good defensive coach. He's better than you think he is because he had a good defense despite the fact that for most of his career they only had one very good pass rusher on the team (Cam Jordan) and for the last 3 or 4 years they have maybe had one good pass rusher (Granderson). He did a pretty good job on defense considering the complete lack of pass rush. It's nearly impossible to play good defense in the NFL without pass rushers but the Saints did.
It's also why his defenses struggled at the end of games. They didn't have an elite pass rusher to take over or shut down drives. QBs had all day to just drive down the field and wait for a defensive PI.