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.