melee is extremely unforgiving compared to ranged, sadly
so is cutting out your own eyes.
yet.
i love melee in pvp
it's just terrible in dungeons
You don't die, you are downed. BIG difference there. And if you do die you can frequently run back and re-join the fight.
Also, if 1 melee attack is killing you then you're doing something very very wrong and somehow managed to break the game and not get any HP when leveling.
Weakness is your friend, reduces all non crit damage dealt by 50%. In case you are bad at math that's almost half! Conditions are the way you win and almost every melee auto attack applies them and melee do a lot more damage than ranged.
Melee is high risk high reward, if you dislike it a lot it may not be for you.
And in regards to doing dungeons, I'm 60 now and I've pugged every dungeon so far as soon as they are available and haven't had to bow out of one yet. All it takes is a bit of determination.
Also playing melee since bwe1 when mobs your own level could put a hurtin on you 1v1 probably helps.
Ok well first of all you can't be killed without going to downed first UNLESS you've already died like 5 times within a minute before that. Which leads back to you not playing right as that should never happen. Second of all, no REGULAR melee attack that does not have a warning will do 25k damage. Sure, a special attack like an ettin's overhead smash will but you have plenty of time to move. Or the grip in AC explorable into the tornado blades of death will one shot you but it can be avoided.
The only way this is possible is if the last bit of damage dealt to you was falling damage as you don't go into downed from fall damage. Or as previously said you've been downed way too many times in a short period of times. Or you got hit with a multi hitting barrage style attack that put you down and kept going to kill you. The last one is designed for you to avoid not withstand.
Other than those reasons you don't go from alive to immediately dead.