[P3D]

The English longbow did not need the years of training in order to get the archers to hit the target. It needed that to build up the muscles to pull a 120lbs+ longbow - resulting in bone deformities found on medieval skeletons.
And you needed that strength to punch through any armor.

As comparison, modern bows are much lighter. Entry-level adult bows are usually around 40 lbs (pound force, 4.54N), the ones used by the average hobbyists are 60-80, be they of whatever type. 40-60lbs bows in the medieval were used by the womenfolk of castles - for hunting and last-ditch defense. And much less effective in combat - shorter range and penetrating power. I was shooting a 40lbs bow and it had hard time penetrate 1" pine from 20 yards or so, FWIW.

OTOH. Get a crossbow and an average medieval youth, with strong muscles from physical work. Longbows have to be pulled by upper body, while crossbows are pulled by (stronger) leg muscles or windlass. You get the range and penetrating power (as in 80lbs+) you need without too much of training and could trump the range and power of any long bow with a crossbow strong enough. Granted, you need the resources to field 3 crossbowmen for each longbowmen for the same ROF - but they would need about the same amount of ammunition for comparable effect.

Of course, if your king orders archery to be a national pastime for every commoner, and your society is suitable for it - e.g. a peasantry not oppressed as much as the serfs in continental Europe thus less likely to revolt - an island nation should go for longbow.

Just my two cents.