The Sark disconnect has become pretty clear. His talent is unable to run his preferred schemes with consistency. It's been his bugbear since he got here to a greater or lesser degrees.
The talent drop-off (or different skill set if you prefer) this year has slapped him in the face with that reality in a way the previous couple of years did not. And seems to have forced some adjustments that we haven't really seen before in the OU game plan and Vanderbilt.
The question then becomes:
Is he too stubborn to see what's in front of his face in practice and game situations
Is he being deceived by assistant coaches as to the actual capability of talent
Is he so distracted by personal matters, the duties of a HC, or some combination that it permits him to maintain his illusions
Or some combination of the three. That he has adapted a couple of times indicates perhaps that he's not so stubborn. Curiously, he has adapted against our more highly ranked opponents and reverted to tendency against lesser opponents, which shows some degree of inflexibility or stubbornness: he thinks we should be able to run his preferred schemes against SEC cellar dwellers, but also "admits" that we can't against top 10 opponents.
I'm not sure hiring an OC solves any of this except perhaps distraction, if it frees him to pay better attention to other things. It might help, too, if that coach is unflinchingly honest with him about what the talent can and can't reliably do. But that can be addressed with assistants other than the OC.