Damage mechanics question

[Kitru]

It's all additive when it comes to % of damage taken/received.

That's entirely wrong. Any +dam or DR effect is multiplicative, which is why stacking tank CDs is inefficient (and why you still take noticeable damage with Shield Oath, Sacred Soil, Rampart, and Sentinel up; 20% + 10% + 20% + 40% = 90%; 1- .8 * .9 * .8 * .6 = 65.44%) and layering your DPS CDs increases their effectiveness. It's been tested and confirmed. I seriously have to wonder what compelled you to think this.

The only additive effects are those concerning chance based effects, such as block, evasion, and crit. Everything else is multiplicative.

Berserk (+50)

Berserk is an increase to attack power, not damage. The +50% attack power actually translates into closer to 40% +dam.