It all depends on the pound of the bow/crossbow and crossbows could, and can, have a very high pound rating since you can use devices to load them.
I have some friends that shoot, and build, medieval bows, and they say it takes a long time to master the bow, compared to the crossbow. They also say that the crossbow is more powerful than the bow.
There are always arguments, but I for one think that crossbows and arbalest should also have a STR-mod since a bow can do 1d12+5 in damage, or even more, if the character is stronger, and that's unbalanced, especially when an archer can shot several arrows per round.
I just don't understand why the constructors made bows the ultimate ranged weapon, high damage and high rate of fire. I mean, it's no use using crossbows since their fire rate i slow and the damage they do does not compensate for the slow fire rate.
Crossbows are good to use as a one-shot weapon, then drop and close for the melee, since you can load it and walk around with it loaded for some time.
I might up the damage a bit on crossbows in my game, more than just the STR-mod, they do take some time to load, especially the arbalest, I'll have to do some counting and see how it turns out, do some playtesting etc.