All potential bonuses

I worded my question poorly. What I meant to say, is that post BB, will this effect be as viable as total damage +9%, because most bosses have a 30% or more damage reduction? Meaning, 30% of that is approximately 10% more damage vs. bosses.

I'm not entirely sure, but i think all it means is the DEF = 0. The thing you're talking about is something called a PDR rate, which is applied after everything. Meaning if something had 50% PDR, whatever you normally do to a monster with no PDR rate but same exact stats, you now do half.