People seem to completely forgotten that he was successful enough special teams coach to get a HCing job. So to that end, I think it was a good hire. We desperately NEED to get better in a lot of the areas of that part of game.
As to the AHC title, my first reaction was that this is a REALLY stupid title to begin with. Aren't ALL the other coaches other than the HC his "assistants" My second thought mirrored a lot of yours. Why was a guy who looked like he was part of the problem get a "promotion" even if its only in a title. It's a head scratcher for sure. But its just a title and Judge is back doing something he is good at.
As for Mayo. He got whatever assurances he wanted when he signed. If it's to replace Bill or whatever it must have been enough or he would have been gone to be a DC somewhere else.
That being said, I wouldn't be surprised if he is named the DC sometime before TC. My belief was that Mayo was coordinating the D last year with Steve being the game day play caller following the defensive game plan Mayo has designed (in collaboration with Bill, Steve and the rest of the Defensive coaches.
As I have explained before, on the defensive side the signal that is given is very dependant on the formation, motions, and personnel groupings of the offense. It's why the D rarely huddles, because nothing really can be called until the offense lines up.