Math.
Leaden salute damage:
Quote:
{[2 * (Your AGI – Enemy INT)]} + fTP * {[152+(WeaponLevel-99)] * 2.45 + (AGI)]} * mab * staff bonus * day/weather bonuses
Wildfire damage:
Quote:
{5.5 * [152+(WeaponLvl-99)*2.45 + (AGI * 0.6)] + [2 * (Your AGI-Enemy INT)]} * mab * staff bonus * day/weather bonuses
Magic Damage+ adds to the expression in curly brackets. You will find that for Leaden Salute and Wildfire, adding 15 to that term is a really small change, whereas multiplying that term with (mab + 0.1) has much more impact.
For completeness, Quick Draw damage:
Quote:
floor[2*(Gun base dmg+bullet dmg)+damage gear]*(staff bonus)*(day/weather bonuses)*mab
The gap is not as big here, but MAB+10 will have more impact than MDMG+15, as well. Unless you're doing weird things in your gun/ammo slots.