Hi Hotspur,
You're probably right, but the deep archeological evidence from all over Europe (British Isles and mainland) shows that longbows were widespread throughout, from the mesolithic. For example the oldest longbow in the British Isles was exhumed from Ashcott Heath, Somerset dated to 2665 BCE (
link).
There's a couple of things going on here. One is the physical size of the weapon itself, the other is fielding contingents of archers. It looks like the Welsh fighters were the impetus for the English longbows.
F