It was said that he was hired to instill a strong defense. Yes, assts do multi-task, but they should all be brought on as a specialist of something. They're not ballboys.
I'll use UK for example. Calipari is the HC and he coaches his but off .. Kenny Payne is focused on developing the big men, Strickland is focused on the guard play, Robic manages the players and makes sure they're gelling, getting schoolwork done and he and Antigua are big time recruiters .. It becomes fairly easy for Calipari to know whether his assts are doing there jobs .. as they have primary responsibilities.