Upon current release, there is no obvious reason using bow over crossbow and staff over wand.

Crossbow movement penalty is almost negligible with all the movement utility skills later in the game and Crossbow already have accuracy bonus; there is really no need to make bow damage inferior.

And for the staves, ever since the Dev introduced wands in dos1, I can't see the reason to use them anymore. To my surprise, they still let the difference stay where it is in DOS2.
Any chance the staff get some nice bonus like elemental synergy, which add 20% damage and -1 cooldown to corresponding elemental skill? This way, wands still get those nice bonus from welding two weapons and staff become more favorable to mage focus on one elemental skill.

Would be cool to see some changes made in future patches.