Combo Barrier Stacks

Steve... his reasoning makes sense. Given any two buffs or effects that modify the same thing, they tend to either cancel each other out (overlap) or one multiplies over the other (stack). It doesn't matter whether Echo gives %-attack and Barrier provides %-protection, the idea is the same.

In particular, there is no other %-modifier that stacks additively the way you described. No stat buffs, damage buffs, nothing - they all either multiply over other modifiers, or cancel them out. (Actually I've never heard of any %-modifiers canceling other modifiers either...)

Also, there is a very obvious case of two %-protection buffs stacking multiplicatively when applied together: cleric Invincible and Magic Guard.

In any case, there isn't much of a point arguing this because it's clear what actually happens.