assby magic res vs add skill

I ask google ai about resistance vs skill... If ai is correct. -1% res = 20+skill.

That means...
Void is + 8 assby skill(+2all) -1 magic res only vs that strong rune word Obsession +4 all + a lot of res, fcr
Void +15% skill damage is less than -1% magic resistance

Guardian's Light -10/+5 is around -9/+25

The +skill damage is very effective against no magic resistance monsters, like cow or other weak monster?


Or....if you have other equip good enough (most of other equipment need to perfect or near perfect) to make 95% magic res to 55-65% magic res

Guardian's Light -10/+5 is around -9/+9-+10
Void 15% = -4 resistance


What do you think about this?

I think it's about right, You can test it on Maxroll: take any magic damage build (e.g.

Nova Sorc). Set a lightning immune monster, like

Grand Vizier of Chaos. Check dmg per second on

Nova spell. Move by 1% the stats of, say, Griffon. Check the dmg per second variation on

Nova spell.

As usual, AI is misleading at best. -1 res isn't "exactly 1%" in any realistic gearing scenario because you're not looking at only one item with possible -res. So your starting point isn't "0 res and then that one item" (in which case 1% would be 1%) but "0 res minus all of the other -res items/skills and then that one item".

Specifically as an

Abyss lock, you easily get well beyond -50 res. At that point, -1 more isn't 1% dmg but merely takes you from say -50 to -51 = 150% dmg to 151% (against 0 res) = 0.66% dmg increase.
Against an immune target, you're hence also not looking at 1% taken from a 95% res broken target but rather 1% taken from a target that is already back down to around 45. So 55 to 56% final dmg = ~1.8% relative dmg increase and nowhere even remotely close to the exceptionally misleading "exactly 20%".

The same shift applies to +dmg as that equally all sums up into a single multiplier. The equivalent dmg is hence equally variable (beyond your arbitrary 1-1.5 span).

As a general concept, final dmg = base dmg * %dmg multiplier * res multiplier. Whichever of those multipliers is still smaller in your current gear set yields more relative benefit when increased by the same absolute amount. Just how much more depends on the difference between the two multipliers. If you're going against high res/immune targets then it will typically be the -res multiplier as target res effectively just gets rolled into that one, making it the only one that can drop below 1 and whatnot. But for magic dmg, you also don't have to deal with too many resistant/immune targets so it isn't anywhere near as prevalent as for a lot of other builds/dmg types. Plus the "res or dmg?" comparison isn't typically 1:1 when evaluating gear as the amount of pts added isn't necessarily the same (e.g. 10 vs 15 on a sunder). That's even more true when considering +skill as the 3rd alternative.