Still Getting One Shot

Hi people,

I'm playing as Elementalist (golemancer), i'm using The Brass Dome Gladiator Plate, 4k hp, 90% phys damage reduction, 8% elem damage reduction (2 endurance charges), 84% elem res, 75% chaos res, 100% spell suppress... And i'm still getting one shot from Mercenaries at maps like tier 13 with no bad modifiers on it...

I just don't understand...

Can some one help me to understand why am i still getting one shot with those stats?

"

90% phys damage reduction

those stats are a lie. it actual not 90%
https://www.poewiki.net/wiki/Armour#Formulas
or use POB for damage reduction calculation

you dont have 90% reduction vs mercs

The phys ones dont do dick for damage. Its the spell casters that consistently one shot players and its because GGG needs to remove pen from their supports. There is no counterplay against spell pen except to walk away which is what I do now when I see pen in their gems.