On the recommandation of @askan94 I have made some additional testing (without rune → with rune):
Naked: 0 → 0
Only plate chest: 27 → 31
Only plates gloves: 7 → 8
Only plate helmet: 17 → 20
Only plate legs: 27 → 30
Only cloth chest: 9 → 10
Only leather chest: 17 → 20
Only mesh chest: 23 → 26
Overall the effect of the rune is just awful. It seems like the diminishing returns rules implemented as of now have slaughtered this rune’s usefulness.
What’s not cool about this is that new EA players would see this rune and buy and equip it, thinking it actually helps when it really doesn’t and just takes up a very very precious utility slot.
It takes a bit more experience in the game to actually go and check the effects of a rune.
I will make a suggestion that something should be done about these runes: either remove them from the EA entirely or change the formula somehow.
Edit: The rune does also say it “mitigates poison effect”, anyone knows whether this translates to some actual DoT duration reduction or something else? NRFTW Tools only lists the Plague res buff.
I can assure you the rune was thoroughly underwhelming before Patch 1 as well. In optimal conditions you can milk about 5% resistance out of it. It sucks early and late.
Mathematically, what you are seeing is the exact opposite of diminishing returns. If returns were diminishing on the enchantment, it would provide a large benefit at low plague resistance and much less benefit at high resistance. This is obviously not the case, as is nicely visible from your numbers.
The rune possibly used to be more functional when separate elemental resistances were in the game, as from the scaling I assume it internally increases the ‘armour’ value that resistances are calculated from linearly.
From my testing, nothing. I compared buildup, decay, DoT strength. Buildup was slightly slower, but that’s likely because buildup scales with damage. It’s just a piddly amount of resistances.