Alibi
I don't know where you get your info from but it is not as simple as all that. A submarine at slow speed will always have an advantage but at higher speeds it becomes blind and probably won't hear a sonobuoy hit the water. Also the buoys aren't that heavy and they are slowed down by paravanes, don't see many sycamore seeds hitting the floor with a big thud!! Anyway during wartime we would only be in the business of tracking a submarine for as long as it would take to get a weapon on it, ROE allowing! ASW isn't just about passive accoustics there are many more ways to skin the cat.
Finally as all of us in the nimrod world have been trying to say the Nimrod isn't just an ASW platform. That is just one of its many roles.
Nuff said! (please)