BUFF and the A-10 require hardened runways - BUFF requires rather alot of runway - Harrier does not.
And I'd like to see anybody attempt to hover BUFF - now THAT would be a neat trick! Or an A-10 for that matter.
The A-10 is all about it's gun - only an advantage if you're facing tanks, which the current enemy do not have.
And BOTH would be eaten alive by the Harrier air-to-air.
AN apples and oranges comparison I'm afraid.