People outside the Kipper fleet were always confused over the responsibilities of a non-pilot Captain.
The captain was appointed on the basis of being the best able to conduct the overall operation of the aircraft, and was in full overall command.
A first pilot to a Nav. Captain was responsible TO THE CAPTAIN for the safe flying of the aircraft. No different to a first Nav being responsible to a pilot Captain for the safe navigation - the pilot Captain still had overall responsibility.
Early 70s I was flying (Nimrods) as First Pilot to a Nav. Captain who told me he had once been in exactly this situation quoted in the OP while a Captain on Shackletons.
His aircraft had ended up off the side of the runway following a crosswind landing. The inquiry asked him
(a) Had he checked that the crosswind was within limits.
(b) Was he satisfied that his P1 was up to date on all his recurrent training.
(c) Was he satisfied that his P1 was not fatigued or suffering from anything that would have affected his abilities.
Since he could answer yes to all the above, he was off the hook.
I quite agree that the key to it all was teamwork, but that applied whoever was Captain.
My recollection of the USN system is a little different to Rossian's. No doubt someone will put us straight. Certainly they normally divided the command, which we found very strange. As I recall,
A Patrol Plane Commander was responsible for the flying but not the tattics
A Tacco was responsible for tattics but not the flying.
A pilot who was responsible for both was a Mission Commander.
To add to the confusion, in the USN the Plane Captain was what we would call the Crew Chief