Damage calculation with Juggernaut and Unyielding

I will admit I am no expert when it comes to this game, but I feel as though I am good enough at math to know that something isn't quite right with my damage calculation. I selected the Juggernaut ascendancy and then selected the Unyielding skill. I expect to see a substantial boost to my damage while I have Fortify, but I only see a difference of a few hundred points.

Am I wrong, or is the game wrong?

Unyielding gives 30% increased damage, which stacks additively with all your other sources of increased damage; e.g. you already have 200% increased damage, now you have 230% increased damage, so the difference is not that big (in my example you go from 300 to 330, 10% more). "More" is multiplicative - and therefore stronger in most cases - where "increased" is additive.

That makes sense in the most disappointingly depressing way. Thank you.