I did not even have 1! second before a Derp Stalker initiated combat regardless which vent I went through. I cannot initiate combat since it is on a CD when you move through the vent. There is not even time to place a single trap or throw a single flare. There was absolutely nothing I could do besides having 70 Persuasion and go through the front door.
Did you try going into turn-based mode before you went through the vent? It only takes 25AP. If you pop Adrenaline on the other side, that's enough AP to throw three grenades - incendiary, whatever, and flashbang, for example. The first two will establish a safe area around you, revealing any hidden creatures, and the flashbang will give you the upper hand on the following turn.
Since your stealth isn't high enough to matter, did you swap out armor and wear a Regenerative Vest? Regen Vests tick their healing without triggering Hyperallergenic.
Do you have Quick Tinkering? Lay down a bear trap. Death Stalkers are melee so all you have to do is be one tiny fraction of a tile out of their reach and you're safe.
You're playing psi, huh? Did you try going through the gate and simply setting up a Force Field? The Death Stalkers will see you through it and come stand right next to it. Since you initiated turn-based before you went through the vent (you did that, right?) you'll have initiative when the force field drops, four turns later. And you'll have had 4 turns to see them, so you'll be able to target them right away.
Did you use Enrage? Death Stalkers don't have an impressively high resolve, so theyre very susceptible. While they're killing each other, you kill them, too.
Did you try putting up mirror images before you started combat? The Death Stalkers don't have machine sight so they'll hit those images and miss you.
Did you use Irongut before combat, so that you could take antidotes in case you needed to drop a few stacks of poison, and still take only a tiny bit of damage from Hyperallergenic?
Sounds like you're just unwilling to do the things that would give you the upper hand. You complain a lot about the Death Stalkers, but they're really very easy. Maybe you should play better.