you are right. it is a theory, but a very plausible one. why do you it took manny a month to announce that he would fix the D by essentially demoting baker and taking back play calling? he could have done that a week or two after the season, especially coming off a bad loss in the bowl game where baker **** the bed once again and put the team in a 21-0 pickle.
i theorize that he was working the entire time behind the scene to land 1-2 individuals, including a DC, to replace baker, rumph, stroud and patke. that's what he did with the offense last year and i think he's smart enough to know that his job is on the line if he doesnt fix the D this year. something happened, maybe something within his control (scheme, autonomy, control) or something outside of his control (other moves).
i'm pretty confident in my theory, and i think time will confirm it. there is no other rational, reasonable explanation.