An excellent post!
The Harrier can do a whole range of jobs other jets cannot.
That is its outstanding and unique contribution to our defence capabilities. Not just the ability to use a fragment of runway, but to adapt quickly to previously unforeseen needs. In 1981, RAF Harrier squadrons were trained primarily to support the Army by taking out Russian tanks steaming westwards across the North German Plain. (With 1 Sqn having a supporting role in the mountains and snows of Norway.)
Then, in 1982, a wholly unplanned and unexpected need to support an invasion task force in the Falklands. Brilliant improvisation, mods such as fitting sidewinder for self-defence developed in an impossibly short time, INAS system adapted to shipborne role, etc.
After that, as you said, Kosovo, Sierra Leone, Iraq and now Afghanistan. Which politicians or planners foresaw
any of those events?
And now, we're told that we won't need any carrier borne jets for at least the next 10 years. The mind boggles. (And forget the smokescreen about being able to operate Frog/Yank aircraft off our new white elephants. The Frogs have a long history of unreliability in "cooperative" ventures and the perennial isolationist streak in the US makes them equally unreliable in time of crisis.)
Reminds me of the political money-saving idea after WW1 that there would be no major war for at least 10 years so that capital spending on the Forces was unnecessary. That principle rolled forward right into the mid-1930s before resources were at last devoted to rearmament - in the very nick of time. What makes today's politicians think they have any more reliable view of what the next 10 years holds by way of "unexpected" threats to the UK's security?