Didn't the dark Eldar remove their psychic potential with genetic engineering though?
I don't believe so. They're just taught from childhood to rigorously suppress their talents, and cloned Eldar have this particularly bad.
And I think that's not anything directly to do with Slaneesh's Thirst or resisting it. It's because Post-Fall Webway Realms are fragile. Uncontrolled or too much use of psyker powers can let daemons bypass the wards using the psyker as a gate, and invade (which makes sense, as using a psyker power means drawing power from the Warp). As a result, the Dark Eldar leadership think anyone developing their psyker potential is too dangerous, and universally ban it.
That's why Dark Eldar kill their peers who try to recruit non-Dark Eldar psykers into their retinue, including in one case where an Archon invited an allied Farseer into the Dark City before. iIRC, a joint operation.
Dark Eldar are, I believe, generally fully capable of learning to be psykers, it's just that their peers would gladly use it as an excuse to murder them if it's discovered, so doing so means you basically have to defect to another faction.
Also, living in the Webway slows the rate of Slaneesh's Curse, so being a Dark Eldar psyker who lives permanently in real space so they can use their talents is probably very expensive in terms of victims, and being an Eldar psyker is very dangerous without the techniques and tools that the Craftworlders on the Path of the Seer use.
There may be some out there, like there are Corsair psykers, but they're rare enough never to have shown up.
By contrast, Craftworlders defecting to become Dark Eldar is apparently relatively common because the Paths are that hard to walk. It's one of the reasons for their declining population IIRC.