Offensive HC is the only option if you make a change.
Let’s say McDermott stays, fires Brady and brings in a new OC.
New OC turns around offense and with Allen at the helm adds a little flair to his play calling, instantly that OC is on the HC train for someone else and the Bills need bring someone else and a new system.
The main reason for KC and Mahomes success long term has been Andy Reid and a consistent offensive system.
Allen has played like crap, wr group is lacklustre but the offensive philosophy and roster makeup have McDermotts meddling stink all over them.