I raided a fishman camp and got something called a "Blowgun". Dont know if its better than a bow or crossbow but raiding those camps do give some neat trinkets
Blowguns, bows and crossbows all have the same [SHOOT_MAXVEL] so their missiles all come out flying at the same speed.
When it comes to ammunition however, blowdarts have 50% of the contact area of an arrow or bolt and so are more likely to penetrate soft armours and lodge in wounds than the other ammunition types of the same material.
That said, blowdarts also have 4000% less penetration depth than an arrow or bolt, so if they do hit wounds, they're not as likely to outright kill anything. This coupled with darts never being made out of metal means that it'll be Aztecs vs Leopard tanks if ever faced with a fully armoured steel Dwarf.
And considering how you'll only ever find darts from subterranean civs, you'll have a limited number of darts to use for the entire existence of your fort. You'd have to ration ammunition usage carefully.
There is however one saving grace for darts.
They're poisoned. It's rare to find a cave civ that hasn't poisoned their darts. Sometimes it can be bumblebee venom, to the more potent helmet snake venom or even GCS venom. If you can seize a cache of the stuff and store it in a cool dry place for a Fortress emergency, you can absolutely wreak havoc with creatures like goblins... Or cave dwellers.