Lets look at the Turner departure from his perspective for a second.

He was not going to be a D.C. anytime soon, as evidenced by the Sirmon hire. He had a chance to go learn defense from probably the best DC around, Chavis. Given that he probably has aspirations to move up he figures that getting some experience under Chavis would help him add to his resume in the hopes of bolstering it for a move up to DC and eventually head coach.

Given that, what was Mullen supposed to do? Should he have made Turner a DC and hired a LB coach instead of Sirmon as DC?

Who knows? But the fact is yes its a lateral move to aTm but he has a chance to bolster his resume for a move up in the future and truthfully there was nothing Mullen could have done that would have been "smart" to keep Turner.