Joint Force Handbags (ah, the joy of Jointry!) is in Afghanistan because no-one else can do the job in it's entirety, encompassing assets available, footprint on the ground, runway type/ length/ state of disrepair in use, ordinance carried, capability, small amount of people needed, etc. The Harriers are the first request from all of the Allies in theatre on the ground because it is the best available to them from all of the options there.
Ever seen a B52 inverted through a pass at 100 feet???
If you are stuck on the ground in a tight spot in a valley in a fire fight- a puffer-jet is the best thing you could hope to see above (or below!) your position.
SMT