Your weapon is behaving normally, this is a common situation when fighters first start using magical P/S weapons.
Magical weapons (like the stump dagger) allow you to hit elemental monsters, but their damage depends partly on your Magic skill, not just your physical combat stats. If your Magic skill is still low, the weapon will technically work but will hit far below its listed maximum.
That’s why you’re seeing 10–18 damage even though the max is 59...
Your scythe hits harder because it relies almost entirely on your P/S combat stats, which are probably much higher than your Magic skill right now.
A few additional things to keep in mind:
- Magic skill affects the efficiency of magical weapons. The higher it gets, the closer your hits move toward the weapon’s maximum.
- Early magical weapons often feel weak when used by fighter builds because most fighters train P/S first and neglect Magic.
- Stump dagger is mainly used as an entry-level magical weapon to deal with elementals until your magic skill improves or you move to stronger magical weapons later.
So yes, training your Magic skill will increase the damage output of that weapon. Many fighter builds train a bit of Magic specifically for this reason when dealing with elemental monsters.