Medieval crossbows, even those with hundreds of pounds of shooting weight, only fired at about 140 feet per second, which was not much faster than the longbows of the time. Its strength, as it is today, was its incredible precision potential, which far exceeded that of long arcs. The two weapons also require a completely different set of tactics due to their respective ranges. A group of longbow archers can stand and decimate an army with crossbows while they themselves suffer minimal danger.
Crossbows are more effective than long crossbows over shorter distances. Longbows could easily be shot onto the shield walls, so crossbows and crossbows due to a number of factors were effectively useless in anything other than direct fire. Still, in a siege, the crossbow is much more effective, so everyone, including the English, used crossbows in the sieges. The range between the two weapons was similar, although the longbow could bow its shots; the crossbow could not do so because the shorter bolt on the crossbow did not remain stable in flight.
The medieval crossbow is much easier to use; most training with a crossbow is how to recharge it and how to use it on the battlefield. The quality of a crossbow may not need to be of good quality, since it needs to be mass-produced, but a crossbow as a fine weapon may have to be carefully designed to fit its user.
