Late to the conversation on this but yeah I’m on the side of thinking that nerfing it is a little unnecessary if not outright stupid. It was already weak, a better thing to do would be to make it a lot stronger but limited in use in battle, losing its efficiency as more health is regenerated, allowing for the player to fight with reckless abandon for a while until their regeneration starts to slow.
And out of combat it’d still be very useful for countering environmental damage as it doesn’t combat tag you, though if that gets too strong it can be scaled down some. This way the stat would be useful in exploration, PVP, and PVE without stalling PVP or making the player unkillable forever. Literally took me 30 seconds to come up with a better idea, shame.
Edit: Just saw the patch note from the goat moochez after writing this lol. That’s a solid solution too I suppose, just doesn’t offer a way to increase survivability out of combat.
I’d rather make it not only strippable by armor piercing - otherwisely people will be forced to use it either way
It should rather be a passive effect like you said - the amount of Resistance invested in determines the strenght of your resistance, and it blocks off a certain amount of damage taken based on the strenght (of resistance)
The more you take damage, the weaker your resistance will be, however the weakening process is slow, therefore making resistance more useful than just “take 5 hits and now your resistance is gone krill fissue bro”.
AP would simply then deal damage THROUGH resistance or reduce it faster based on the percentage.
I mean, sure, it has good initiator potential - but when you get resistance turned off - doesn’t it just become useless?
You take several hits without much damage and then you suddenly take full damage because they are using AP?
At this point Resistance would be used below 20% since if we invest more you will lose onto other stats, therefore making armor piercing users your biggest enemies
(mage better)(surge is a healing spell now 
)