But that was exactly why it was still the best airframe for the job, as the early design was so overengineered for a civilian airliner, that it was so good for the job, especially at low level in dirty air over the oggin.........which is not something any of the newer anti-sub airframe design like the P-8 can cope with.
The biggest issue that caused the delay and subsequent cancellation of the MRA4 version, was the MOD reducing the numbers that forced BAe to come up with the daft fudge of suggesting re-using existing 60's built MR1/2 fuselages instead making the whole thing new build. It was a unsound engineering decision to appease MOD bean counters which ended up causing massive delays and costs which were more than if they had just built them all new build.
It was a classic case of accountants overriding engineering for a short term financial gain that was only ever one on paper and ultimately cost the MOD billions.