I mean you see in movies so often so it no longer even surprise you (especialy lately) as Hero gets horrible beating, and then he "catch a second breath" and stand up with new power, even stronger than anyone could possibly imagine.

So i guess i allways seen 50% effects as just empowering this "second breat / adrenaline pump up" thing.

I agree with you on this one.
An axe that could feel the rage of a wounded fighter through its hands to deal "+xDx damages" would not be so wtf to me, but with a few IF :
- If it was a single item. There are way too many items with this conditions in BG3, including a full set of armor.
- If it was a usefull weapon all the time with an additionnal bonus under specific condition.
Lots of items + gimmicky item does not help to make them "believable". It only serves the gameplay, a gameplay that (as Etonbears said) most players will try to avoid.
A helmet that gives you +1 bonus action (makes your character faster if you're wounded than if you're not)
An amulet that makes you avoid AOO (makes your character faster if you're wounded than if you're not)
Gloves that gives you fire resistance (makes your character more resistant if you're wounded)
An armor that gives you +1 damage (an armor that makes your character hit harder if you're wounded)
A common greataxe that only deals an additionnal +3.5 damages if you're seriously wounded.
2 common shortsword, a common greatsword, a common longsword and a common heavy crossbow that only deals an additionnal +2.5 average damage if you're seriously wounded.
Just get rid of these armors and the greataxe + upgrade the Githyanki weapons and everything would be fine IMO. +1 weapons with +1D4 damages if you're wounded.
Easy explanations (not sure there's a lot of lore yet about githyanki weapons, but I may be wrong), usefull weapons or at least equivalent compared to those you have already found, powerfull weapons if you're ready to handle a hard condition.
I could also have said +1D6 rather than +1D4 because I'd enjoy so much to find +1 weapon dealing +1D4 "element" damage without any conditions in act 1...