Crossbows and bows are much better. Why slings,darts and throwing daggers I cant understand.

Darts and throwing daggers add your strength bonus to their damage, so for fighter types they can make a powerful opening volley. As for slings, I'm not sure, maybe to provide ranged bludgening damage against opponents that have resistance to peircing.

I noticed that bludgeon damage causes extra damage to golems skeletons etc it's useful.

I particularly don't like darts in IWD2 as mage weapons. Why? First time I tried them out, I happened to have all 6 members of my party switch to missile weapons to get in a shot or 2 at an incoming mob. Of course, I had my mage using the darts for some silly reason. Well, due to the short range of the darts, the mage runs out in front of the rest of my party to throw the darts. Ooops!

My spellcasters stick with bows or crossbows now. I want them to stay in the back of the formation.

I think that slings also add in the STR bonus. They certainly seemed to the last time my paladin tank used one on a boneguard, doing mid-teens damage.

Another type of weapon that's a very worthy ranged weapon in IWD2 are the +2 returning throwing hammer. Excellent range. +2 weapon. Base damage is crushing damage. Extra electrical damage. Very nice weapon for a tank. No need to manage ammo.

OTOH, I really dislike non-returning throwing hammers (or axes for that matter).

1. Throwing hammers are heavy. 10 throwing hammers are VERY heavy!

2. Why the heck can't you just go pick up throwing hammers or axes after a battle and reuse them? Are they that fragile that they are legitimately single use only? (I find this difficult to believe.)