Truth is that going from 50% to 75% really is more than a +50% damage reduction.
Let me explain, what i think is misleading you is that you are treating percents as flat numbers.
I think that using a flat 100 monster damage brings to misleading and makes 75% resists appear like it is a 75 flat value then used to perform a formula like 100 - 75, which is not correct:
The real operation is not 100 - 75 = 25, → the real operation is 100 * 0.25 = 25
Percentages are very different than flat/raw values, percents can lead to crazy scalings and needs to be looked from the EHP angle (to normalize it into raw/non percent) to understand how strong it is, it needs to be evaluated as the whole HP + Resist formula ← that is Effective HP (EHP)
Let me (hopefully) show how strong percent resist shows to be when correctly displayed.
I will use some more “spurious” values and put a couple constraints:
STEP 1 Primary stats: life and resist
. Life is fixed, i choose 9000hp to make it harder to confuse it with “100” values
. Res is variable
9000hp 50% resists → EHP is 9000 / 0.5 = 18000hp
9000hp 75% resists → EHP is 9000 / 0.25 = 36000hp
9000hp 80% resists → EHP is 9000 / 0.2 = 45000hp
9000hp 90% resists → EHP is 9000 / 0.1 = 90000hp
Without much doubt:
**From 50% to 75% resists the EHP value has doubled **
**From 80% to 90% resists the EHP value has doubled **
^This is very important to look at it this way, because what follows is what happens in games
STEP 2 Next stats: damage dealt/taken in a single hit
. Damage dealt is also fixed. There are thresholds of damage that we can take and are directly dictated by the percent resists.
What it means in practice:
**9000hp 75% resists will survive hits of up to 36000 **
versus
**9000hp 90% resists will survive hits of up to 90000 **
Or the other way around:
**More than 36000 monster damage is will kill 9000hp 75% res **
versus
**More than 90000 monster damage is will kill 9000 90% res **
^36k vs 90k damage difference
STEP 3: DPS and damage healed + health sustain
This is what I kinda think ARPGs do wrong with few exceptions.
In LE monsters deal huge slams, scaling is out of whack, once you stack 3 mobs spamming killer slams you get x3 fuckd up
In PoE oneshots + exp loss are deliberate and by design to kill bots and macros/scripts (IMO of course). Monsters are also oneshotted by players, final bosses included are nearshotted in PoE.
GD seems to be one where they do it right, chars HP and EHP are well within control of players, monster packs size and damage is scaled right and all within their ilvl and you will know when you got dpsed down to death. The dps system is so well tuned and understood that GD has healer monsters no problem HEH.