yes all moving surfaces were first used on the un-flown Miles MACH 1 design which us Brits gave to the US government in return that our scientists would get some research info. In practice the UK gained nothing from the exchange - but the US took all the ideas from the Miles program and used a hell of a lot of the techniques on the Bell X-1.

The reason for all-flying surfaces is that at the point of entering supersonic flight, compressibility effects produce control reversal - the tailplane/fin flexes the wrong way, so that up means down and left means right etc. V. Nasty for a lot of pilots with conventional surfaces in the early days of supersonic research.

The Bell and the Miles had all-flying surfaces.

Think of it this way: re models/ sub-sonic planes: Flaps on wings increase the total lift a wing can produce by increasing the effective camber of the wing. If all-moving surfaces were better (i.e. more powerful) then you would be able to get the maximum lift out of a wing just by pulling the nose up indefinitely - and adding flaps wouldn't increase the lift co-efficient. However, to get the maximum lift co-efficient from any flying surface you are far better off changing the camber in addition to just changing its angle of attack.

With blown surfaces like rudders and elevators, you might gain even more control authority by changing the camber (having a flapped control surface) as well as making it all moving. The ultimate would be a leading edge device, a trailing edge device AND the ability to change AOA.

However you are looking at heavy servos and heavier structures which make this option less viable. As the weight of the tail increases I suppose to some extent you have to have more powerful controls to get snappiness in aerobatics....