Talking X's and O's with peers is a lot different then teaching them to college kids. I have a major problem with the "everyone says Detmer is so smart, even Brett Favre." What does that matter? That's not coaching.
Second - Tayson and Tanner have been identical under Detmer. Both struggling to make plays. Both inaccurate. Both shadows of what they were in a previous system. When it's consistent between multiple QB's, both of whom you've seen succeed, it tells you something else is the issue. Common denominator is the system.