Well I was doing a stealth run and I was in nothing but my underwear and I can tell you that even with a full stamina bar one or two hits and I was almost dead. So armor is needed, but stamina is key. I am often surprised during a heavy fight that I have not lost any health, due to maintaining stamina. But after the fight my armor will be trashed. So I guess you could look at it like this.
If you have no stamina it does not matter what you are wearing you are going to die fast.
If you have stamina your armor, well acts like armor, until it is completely broken, as long as you have stamina you will not take damage, if your armor is above zero.
No armor you take massive stamina damage as well as health it seems and two or three hits and your done.
So keep your armor repaired and don’t overdo it in combat.
At least that is what it feels like to me.