Yes, I agree. If we want to have the closest DPS (normal/physical and elements) we need to select an enemy to apply amor, resistances and also special modifiers of the weapon such as Holy2. In your example, I would say that
Paladin's Longsword should be 8.8 normal DPS + 6 Spirit DPS against normal enemy type.
Paladin's Longsword should be 12.8 (8.8 + 2*2) normal DPS and still 6 Spirit DPS against undead enemy.
Paladin's Longsword should be 12.8 - X damage reduction of armor 20 (I need to do the math) and 4 Spirit DPS (6 - 30%) against Old One (undead) enemy