When I did this quest as stamina nightblade, I died few times too. However, the key was to get npcs to attack one atronach while you kill another and then get the second one. I would sneak right before they come out and then would kite them by npcs so they would get one of the atronachs off me. At least that worked for me.
I've seen lots of complaints on this since One Tamriel. I think it got harder owing to the way the One Tam mechanics work. Make sure your gear is close to your character level...when these move apartmyou get increasingly squishy.
My main is a stamblade. Kiting (running like heck) helps. You can lay down a lot of damage from range w bow abilities, light attacks, and the spectral bow from merciless resolve. Just remember that storm strong has are immune to poison...choose abilities that aren't poison based. Caltrops would be good here, or rearming trap.
Also buff your dps as high as possible. Be a minimalist in this fight...use fewer abilities and more buffs. Get major brutality from rally (2h) or shrouded daggers. Get the 8% damage boost from merciless resolve. Make/get potions with three helpful buffs and use at the beginning of the fight. If you can slam One into the ground fast, the fight is over.
If you have it, the bow or dual wield ultimates are both helpful. And attacks in dw that provide health back. And every once in a while, bolstering darkness is just a necessity as an emergency ultimate.
As it turns out, I was finally able to find someone else who was also trying to finish the "Breaking the Shackle" quest, so we grouped up and were finally able to defeat Storm Atronachs and thus, the quest.
Hopefully there's not much left to complete the main story so that I can then move on to the DLC's.
In addition to what the others said, self-heal is key for squishy stamblade. If you have, use Vigor from Alliance War, otherwise the bow skill that heals you after stun ends, and the two dual wield skills that put a HOT on you when doing damage. Also use Killer's Blade to finish (smaller) enemies, you get a strong heal when they die.