He's conservative, not defensive-minded.
Chan doesn't get blamed for the defense. He gets blamed for who he hired to run the defense. He managed the offense and did okay, relatively speaking.
Marrone also shouldn't get credit for the defense, just credit for who he hired. He also manages the offense (with his sidekick) and the offense has been abysmal under his watch.
He's a poor head coach and if this team ever wants to go anywhere, he needs to be replaced asap.