Your starting assumption is that Marrone is a good head coach.
If you're a Jacksonville fan, that's an odd starting assumption. You've had a bad head coach for a while. Wasn't a big secret. Now you tell that fan that all along you had a better head coach, and you gave him the responsibility of coaching the o-line. But really fans, he's better. Let's put aside that as he is better, we maybe could have given him more responsibility. Even though your offense wasn't particularly good, suggesting this better head coach had limited impact in the role you placed him in, fans should expect the team to get better now that he's in charge.
If you believe in Marrone, you'll buy it, not for any logical reason, but because you believe in Marrone.
I think this is a really tough sell to Jacksonville fans. Odd situation. Usually you make a continuity hire when things are going well. Things haven't been going well for Jacksonville.