Crossbows are so powerful in real life, that at one point the Pope may have banned their use against other Christians
wiki. As for penetration, there is a famous case of a knight being stapled to his mount by a longbow arrow.
So the idea that the penetration of DF armors by missle weapons is just plain unfounded. These weapons are that dangerous.
However, they do have a serious fault. As has been mentioned, the rate of fire is just ridiculous, so much so that I call them my assault rifles. Each dwarf whips out their 25 round clip and fires a burst into the goblins' ranks. Cutting the Rate down to 1/2 to 1/4th of its current setting would balance things well.
BTW I have plenty of victories of footdwarves vs goblin bowmen. The key is to provide the footdwarves with something to hide behind as the goblins approach. For instance, under my road in several locations I have small 5x5 bunkers. These are the rally points to squads with "chases enemies" off. As the goblins pass overhead, I switch the "chases enemies" on, and boom - macedwarf ambush. The next generation involves a chokepoint with a bridge over the bunker. When the bridge opens, the goblins drop (and are stunned for moments) into a pit of dwarves...messy.