Note the swords the archers are carrying, this is a depiction of longbowmen at the battle of crecy.
As for Eastern archer types, not only were they lightly armed and armoured, but they were also mounted. As far as i can see, nowhere in Medieval Europe, did Archers equip themselves with heavy armour and weaponry; at least not as a mainstream fighting style (obviously there will have been the odd mercenary brigade of highly armoured archers, but as M&B really depicts the fighting styles of certain nations/cultures around Europe, then you cannot have the archer as an armoured heavy armed force, unless of course they were mercenaries.
By all means the very top tier units should have medium studded leather/scale/light mail, but as for carrying Voulges? No, that is not right, it just didn't happen. Voulges were heavy weapons, they are heavier than they appear, and carrying one of those on your back restricts your ability to fight. Not only this, but if an archer was mounted, he could not really carry it whilst firing a bow. If he was not mounted, like most western European archer companies were, they would prefer to travel light, simply because they came from poorer backgrounds, could not afford horses, and therefore had to march with the army (ok maybe it didn't have that much effect whilst marching etc.)
But any Medieval commander knows that archers need protecting with infantry. Thats why archers were not that well equipped, because they were protected by infantry, which meant they didn't need to carry heavy weapons. Yes a sword and a small shield is sufficient. But if the infantry line is breached, and the archers are imminent for melee combat, any archer will have regretted bringing a voulge or similar heavy weapon. They needed to travel as light as possible to skirmish, and also if needs be, run from the enemy.
As for the crossbowmen of western/central Europe, yes they were well trained in melee combat. The crossbow was often a secondary weapon, not a primary. But the crossbow's versatility and no need for extensive training and practice meant it was the weapon of choice for a large proportion of Medieval armies.
So to sum up, yes, archers are overpowered in melee combat. and no, crossbowmen are not overpowered in melee combat. But regardless, the crossbow's inadequacy compensates for the melee strength.
So by this logic, in order to balance the archer units, bows and arrows need to be strengthened, proficiencies need to be extremely high (i'm talking 200+ as archers in Britain and in Eastern Europe practiced with bows from a very young age). This has to be done first before their melee ability is reduced. Archers are very weak on this game. In real life it should take no more than 2 arrows to kill a poorly armoured man, and a little more to kill those that were armoured (although they should be ineffective against plate). Also, do bodkin arrows have some sort of bonus against mail? if not, why not? All these factors need to be taken into account. As for weaponry, they should carry a one handed weapon, with some having small shields (not all though). The Nord archers should vary a little, they should carry from short swords to hatchets and small hammers/mallets, but nothing too heavy, and certainly nothing two handed.