the Harrier FEaR was 18 so yes, it could have achieved this
I'm sure it could, but for how long?
As you allude to it was the reduction in size to 2 sqns that was it's ultimate downfall - to have reduced the GR4 to a similar level in order to save the Harrier would have meant that whilst we would have had flexibility and agility we wouldn't have endurance (in terms of length of an op rather than how big the pee bag is
). And one thing recent history has shown us is that supposed non-enduring operations swiftly become enduring.
Lets hope we don't make similar mistakes when it comes to procuring F35C. Buy enough!!!