I can’t think of another time that a coach voluntarily left a team for a lesser role somewhere else. Obviously Staley is the real DC and Hill just held the title but still if the goal is to eventually be a HC why would you want to go back to being a DB coach? Only reason I can think of is that you have such little confidence in your coaches system that you’d rather your name not even be associated with it.
Which is honestly a smart move for Hill. Nobody is going to hire anyone associated with this defense.
See the Chiefs this season. They’re still working out the kinks but Reid is always a step ahead of the defensive meta. I guarantee if the Chiefs and Dolphins meet in the playoffs KC will torch them, unfortunately.