I played throwing, archery (and HA) and now doing a dedicated xbow (150 wpf in xbow) and I can tell that the hardest range class to play is certainly the dedicated xbowman. Even with 150 wpf, it takes a good 3-4 seconds to reload a sniper xbow where your sitting duck if you dont have teamates to keep ennemies away or if your not hidden. On top of that with the slots nerf coming, heavy and sniper xbow will be 2 slots with 1 slot for bolts which means only one slot left for anything like a 1hander to defend myself in melee. Archers can move while reloading and shoot on the move so they are less vulnerable. Throwers can hide behind a shield and even with a shield, they can have 12 ammo with the best throwing weapons (beside lances) but me, if I have a shield (or a 1hand weapon) I only have 15 steel bolts with my heavy or sniper xbow. Just saying...
So IMO, a little damage bonus would certainly even things out.