Skill determines the hit chance. Mage weapons use either your magery, or the skill required for the weapon, whichever is greater.
A char with 120 Magery using a mage Weapon -20 would hit the same as a char with 100 Swordsmanship.
Damage is modified using strength, anatomy, tactics, bonuses, etc... It's not determined by the hit chance.
Tactics is required to use special attacks.