If you have 100% of necrotic damage taken as physical on your armor, does that make necrotic resistance obsolete? Or does the resistance first reduce the incoming damage before it is taken as physical? ty
It makes it obsolete.
It makes necro res insignificant. All incoming necro dmg will be count as phys and reduced by phys resist
Also armor will become more efficient vs necrotic dmg dealers
Resistance doesn’t reduced damage, they reduce -75% zone level resistance penalty. What you see in character sheet in calculations of damage is 0% not 75%. Conversion for “damage taken” come first, so necrotic damage conveted to physical first. That include hit and dots too. Sentinels helms, body armor and idols are op for defence, you can convert 100% void and some of cold to phys and make abberoth fight more comfortable with armor capped 
True
Preventing extra dmg is kind of reduction 
About Abby - VK could deal with incoming void dmg with new passive node
Abyssal Fluctuation
Elemental Damage Taken As Void: 10% per point
Void Damage Taken: -4% per point
Also threshold node in first column on upper one provides 5% less phys and void dmg
It is indeed absolutely a reduction, as without it (or with less of it) you’d take more.
It does. How much damage do you take with zero resists versus capped resists?
I mean you don’t need to use 75% reduction on damage calculation. This is confusing thing in LE. If you resistances 75%, treat them as 0% in formula. Anyway, It’s better to have more resistances for debuffs like mark of death or shreds. 25% for mark and 20% or something others I don’t remember