He asked Morris to run Staley's defense.
Don't think he has no influence on the defense.

This is similar to offensive minded college coaches.
They want a particular defense to be run that would work synergistically with the offense.

This is why you have some coaches that ask for 2 high shells.. because they know they can score TDs and just need the defense to hold to scoring at the red zone. And then you have others that go aggressive thinking that they can gamble since they know they can score TDs on offense anyway.
2 different philosophies.. no one is really right, but it is dictated by the HC usually if they are the OC as well.