How much tankier would I be wearing this? Seems underrated to me! POB doesn't calculate it well

Opportunity cost: while wearing this you are not wearing a 1200 ES chest, or a 200 life & life %, or a +1 level Corrupted gems, or a Covenant...

The 380% increased armor and evasion is a local mod, meaning it only increases the number on the item itself (would be like 200 armor without this mod).

The thing is chance based defenses is that they are, well, random. Its not really HC viable and in softcore most people just don't care and rather have 10% more damage tan not die occasionally. Also the chances are quite low, so you would need other sources of it to be actually viable but I don't know if those even exist. Also i am sure its capped to 75% chance to avoid, so would still take the full damage in every 4th hit and die to it. If it doesn't kill you you don't need to avoid the damage in the first place...

I think this could be good on my witch hunter, I have a big presence area of effect so the damage boost would be nice. I think this could be good for bursts of attacks from a group of monsters, not sure if people actually use this but I'm wondering if the ehp would be a big jump compared to a regular armour/evasion boost.

I kind of refer to these items as the "noob traps"

If you're unfamiliar with itemization or general balance the items look insanely good. But the more you understand the game, the more you realize they are fundamentally useless, unless they were to release something later down the line that pairs with it.

Any decent optimized rare chest piece would blow this thing out of the water for defenses, not to mention there are a number of unique chest armors that also would vastly increase your chances of survival compared to this.

It's not good yet, is the best way to look at a lot of stuff in the game imo.

It's a little difficult to say without knowing any other details of your character, and it depends on what you mean by "tanky", because there's raw HP/ES, mitigation and avoidance and they all can make you die less in various situations.

I will say, I think most mobs generally do physical converted to something, so for base content I think this would be fairly underpowered. But I think if you're often running maps with say, double gain as, I think this chest would actually be decent if blue life wasn't overwhelmingly the best choice for tanking up.

PoE2 is still fairly new as far as balancing goes and it's just too difficult to beat a 1,000 ES body armour in the current meta because we generally don't have enough base life for avoidance layers to matter. With Sorcery Ward maybe that doesn't matter, why not give it a try?

I don't think it's a HC vs SC issue, because it's not so simple that avoidance is bad (is EV bad?), ideally the game would be balanced around not needing 4k+ ES because once you can be sure that you have enough base life and recovery, avoidance actually becomes really good. If the balancing is adjusted you can be sure that HC players would consider avoidance (not necessarily this armour) if it made sense in the meta.

% chance to not die isnt good as the build wont feel consistent. But also, thats damage from HITS not all damage.

It's good for anything that already mitigates damage by stacking chances of reducing getting hit, i.e. Block and Evasion. If you incorporate this on a hybrid Evasion + Block build, you will add another layer of defense in that chain. Outside of that, it's just too random. While it does avoid damage, it applies after Evasion and before Block. It's additive with modifiers that do the same thing, i.e. Aspect of Stone (in PoE 1). PoE 2 currently does not have other such modifiers (yet), not as far as I'm aware.

Refer to this: https://www.poe2wiki.net/wiki/Receiving_damage

This type of defensive layer happens at step 6.3.

50% , u die or u don't

Eh, I'd say it might be ok to use with sorcery ward as that is a limited supply lifepool and the only way to restore it is to not take damage for some time.

Other than that though I don't think it is particularly great but it does depend on what you want from your build. If you a clearing the screen when mapping then the main advantage of avoid will be lost as its strong against lots of smaller attacks.

Try it and report back how it feels. There are certainly better options end game but for leveling and early maps it seems decent. If you have some block evades stacking nonsense for fun then go wild with it.