My real issue is the number of failed regimes he's been associated with
This.
I am a huge fan of Dunc, as a public figure, as an avatar of the Club, as an all around salt of the earth guy (albeit one with a history of violence in service of club and defense of home, which is a feature not a bug for Mrs. THBJ).
The coaching record at the club during his tenure is not very good. Not only has the position in the table been generally unsatisfactory, the players haven't distinguished themselves so as to show they've been well coached. There was an uptick in form in set pieces, but that was the work of Davide Ancelotti and its was terrible before, terrible afterwards. DCL went from a squad player to a breakout star and Dunc was credited with his improvement, but we still don't know how sustainable, and DCL still struggles with the ball at his feet. Otherwise, there's not much that's been positive.
If he doesn't want to manage, that's fine. If he wants to coach - ie to teach skills, tactics, etc. -, ok, but even for that he probably needs to go somewhere.
If he wants to be just a totem for Everton Football Club, an ambassador, a public face, a cheerleader - and those are all great things - let's hire him for that. Let's have him in the concourses and the streets before and after the match, let's have him on TV, let's send him around the world to supporters' clubs events. Fantastic (not sarcasm, it would be great). What I suspect we have, instead, is that sort of role, in the guise as a coach. But we need better coaching.