I consider this as a bug as it is unlikely to be intended.

On any weapon the damage is in creased by either a type damage increase, like "50% Material damage on attack with this weapon", and/or by specific damage skills, like "106 fire damage on attack with this weapon". With some luck you can add one of those via crafting or gain one by improving the rarity via the Black Market.

This is not possible for staves! There is no "50% Occult damage on attack with this weapon", not even the Material version as it is common for melee weapons and pistols. Staves only have a general spell damage increase, like "90 fire damage added to spells" which do not contribute to the damage of the staff.

There is one exception: The unique staff Chrone Cell, which has the skill "Aether Damage on Attacks with this weapon".

My suggestion here (I've suggested already in another thread the introduction of Wands):
Allow staves to have either spell rather than physical base damage, or, even better, allow damage on Attacks with this weapon, specific damage like shadow, sacred and aether as well as general damage like Occult, Elemental and Material.

Cheers Euclid