Alright here's a Safety First Final Resistance fucker.
Other than the glitched armour calculation in the first one (because she has 0 pre-armour incoming damage), you can see fire SP does get around the % reductions, but armour is actually pretty strong so you still don't hit all that hard even with 550 Fire SP.
I do have the 5-piece flame negoori set though, so I do 550 flat fire damage at the end of each turn in an AOE which can't be stopped. If I had Fire Bolt as well it would add up to quite a lot to supposedly hard-to-damage enemies.