A small note on the supposed downpour weakening Italian X-bows more than English longbows.
29th October at a historical congress in Cph on something else I chanced to learn that experiments with submerging X-bow strings in water for 24 hours before using them showed no difference in performance to dry ones. Likely the poor Genoese used that explanation as one of many to explain how the volleys of English arrows mowed them down while they could not reach the longbowmen placed on a hill with their own arrows.

IMO the explanation is more likely:
1. sheer volume of arrows, the longbow has a higher rate of fire by far.
2. better range from the hilltop.
3. The Genoese had not brought their pavises to hide behind.

Anyway, this hints at why the English archers were so effective, they were trained for a lifetime to mass-fire volleys and their sheer volume of fire was incredible. Further, they used the armour-piercing bodkin arrows, which earlier archers did not. Both these developments only happened after the Welsh bloodily demonstrated how scaringly effective longbows were.

Now, the army bog finds from Denmark has yielded longbows, but not many compared to the number of spears and even swords- only in one of them are there lots ow arrowpoints AFAIR, so perhaps massed archery with longbows did not play a large role in Germanic warfare.

Rather we can turn to the situation 1000 years later as decribed in our first medieval sources purpotedly telling of prehistory, Viking Age and their own Early middle age.

Now whether we see them as relating truthfully the stories of the Germanic Iron Age and Viking Age, or (as later artists depicting New Testament events did so with them wearing full plate etc), is not so important here. What the Sagas and Saxo relates is that archery was more comparable to current day snipers than mass weapons.

Let me present a piece of Olav Trygvessons Saga, written by Snorri.
At The Battle of Svold where Sven Tveskæg (Forkbeard), Olaf of Sweden and Erik Haakonsson, Norwegian earl in opposition to Olav Trygvesson confronted him in a battle and clears his warships one by one (clearing a ship in the Viking terminology means boarding and killing everything). No one can board the Royal ship; the famously huge "Ormen hin Lange" (The Long Wyrm/Dragon) as long as Einar Tambarskjelve shoots his huge bow "Tambar". From this high vantage point he can pick off everyone that tries until Erik Haakonsson gets his "Finnish" (Samii) archer to shoot back*.

Einar shot an arrow at Earl Eirik, which hit the tiller end just above the earl's head so hard that it entered the wood up to the arrow-shaft. The earl looked that way, and asked if they knew who had shot; and at the same moment another arrow flew between his hand and his side, and into the stuffing of the chief's stool, so that the barb stood far out on the other side. Then said the earl to a man called Fin, -- but some say he was of Fin (Laplander) race, and was a superior archer, -- "Shoot that tall man by the mast." Fin shot; and the arrow hit the middle of Einar's bow just at the moment that Einar was drawing it, and the bow was split in two parts. "What is that", cried King Olaf, "that broke with such a noise?" "Norway, king, from thy hands," cried Einar. "No! not quite so much as that," says the king; "take my bow, and shoot," flinging the bow to him. Einar took the bow, and drew it over the head of the arrow. "Too weak, too weak," said he, "for the bow of a mighty king!" and, throwing the bow aside, he took sword and shield, and fought valiantly.
It is, BTW, interesting to see how the 13th century struggles of Norway vs Denmark and Sweden is reflected in ethnocentric bias, just as the Danish ones against the Holy Roman Empire is in Saxo.
Anyway, there are many stories such at that in various King- and Family Sagas, Saxo, etc., Gunnar of Hlidarendi for example, holds off his attackers by archery and is a famous archer. So we can conclude that in as much as the written sources reflect the real situation and are not just emphasising the prowess of a few great men (which they also do), archery was more of a sniper-ish nature.
However, there is at least one instance where archers in more numerous nature is present, last battle of Harald Hildetand at Bråvalla where amongst other things, archers from Telemarken take down the hero Ubbe of Friesland.

That leaves us little to conclude upon really, and my tentative interpretation would be that massed archers could play a role, but that only specialists such as Finn, Ejnar, Palnatoke, Gunnar and the men of Telemarken (but not Olav Trygvesson) employ the warbow/longbow and has specialised training with it.

*interestingly enough the most famous and highest scoring sniper we know off is a Finn, Simo Häyä 522 kills in 96 days of The Winter War, and Saxo describes the Finns as using basically the same tactics in Viking times as they employed in 1939...