There has to be a head. You can't have someone running something and their nominal boss having less power than they do.
Now, could I see Zo being the Asst AD with a tacit agreement that Jurich grooms him to be the AD down the line? Yes and that would be a solid arrangement. However, Zo may not want to wait his turn and may want to be THE MAN. There is also the power dynamic of Zo being a former player and probably untouchable if hired. What happens if Jurich and Zo disagree on the direction of the program? Who wins that battle? Jurich is an outsider..