Here we go
(Disclaimer; I study 15th century Europe at uni)
Yeomen arrived around Henry VIII when the longbow was in decline. The longbow was last used in anger at Flodden (1513) where the Scots in their 'plate'* rolled right over the longbowmen and slaughtered them. The arms/armour pendulum had swung and the armour was invulnerable to arrows. Before that you could call them 'Franklins', but really serfdom went out of use well before The Black Death in 1365 and the labour shortage removed it almost entirely.
By law most sports were banned during the longbow phase in England and peasants had to practice the bow instead, this happened every Sunday. This may sound kinda hardcore, but legislation like that was in place all over Europe. The Swiss had their crossbowmen who were frighteningly accurate, deployed off horses and rode as skirmishers. They too practice pike, halberd and crossbow every Sunday.
The reason for this training wasn't accuracy, although that was certainly a by-product, but like most military training it was endurance and team building. Archers had to be taught how to function on a battlefield, and the vast majority of rural people in Europe were not notably military minded. In fact it was a widespread view that urban troops were the best, as they had a natural cohesion because of their subculture of guild membership.
The reason bowmen were valued is that they were very, very cheap. Just like in Twilight 2000, its the guy with the most cash (logistics) who is going to win. Most wars ground to a halt because the attacker ran out of funds and couldn't pay their troops. There was no logistics system as we know it now; the logistics were handled by free agent merchants who followed the armies called 'sutlers'. If you ran out of cash they simply went home.
For example, at Agincourt the archers were armed in padded jacks (actually very, very good armour with the drawback that it deteriorated on campaign). At any one time they outnumbered the French men at arms engaging them by
at least 2:1 in a defensive position (so it's tactically like 8:1). It is estimated(1) that the archers ran out of arrows very early in the battle and fought as medium infantry. These men were professional soldiers, not feudal levies, and fought campaigns for years at a time if paid.
The vast majority of significant mediaeval engagements were sieges. Here the crossbow reigned supreme. The crossbowmen would sit behind his hoarding, pavise or gabion and await his shot - the precursor to the modern sniper. Sappers had to wear massive siege armour twice as heavy as normal plate, to survive this lethal environment. Fleeting targets were the norm, and the time to draw and fire was usually too long to get a hit. In fact, most soldiers never saw a pitched battle.
The ratchet crossbow, or 'crannequin' is simple to make with rudimentary tools. All you need is a supply of seasoned wood and good steel, something both in abundance in twilight 2000. I can make you a crossbow out of a car spring in an afternoon, and the crannequin in maybe two days, given power tools. This weapon can be spanned** in the prone position, in a car or in a tree; all useful qualities where the opponent may have a modern assault rifle.
It does take some experimentation to get the crossbow right; the stock ('prod' or 'tiller') has to be a certain weight to take the recoil. Spanish troops complained that their crossbows were 'en dente'*** or 'had teeth' they kicked so hard.
Finally, a word on penetrative power.
The steel limb crannequin put out phenomenal power; enough to blow through maille armour. Around 15kg/cm. That's fucking insane power, and will penetrate any body armour the PCs wear unless it's 15th century two-stage annealed steel.
However, to whet your appetite, the
espringalde box siege crossbow (about the size of a KPV machinegun) put out 1500kg/cm . . .
* 'Cap a' pie' or 'white harness'
** This is where we get the term 'spanner' from. They were used to tension crossbow limbs.
*** This, of course, isn't Spanish. I assume the chronicler wrote it in Latin.
(1) Curry, A
"Agincourt, A New History" (London, 2006)