Bacon Bits
Legend
Both buttons produce $1,000. Even in the novels, Psionics was never really important to the setting. There were characters who were powerful with Psionics, and the gameline expected people to know about Psionics, but it has no narrative importance. It's just a thing people have. It was never even "the hard work path to power" since everyone in Athas has some amount of psionic power.
Magic was important to the novels in that the Templars and Sorcerer-Kings had it. In that Borys and Rajaat had it. In that using it was inherently destructive. In that there was always dramatic tension around Sadira because she used magic and toyed with defiling, raising suspicions around her loyalties. It's been several years since I've read the Pentad Prisim, but I recall Agis's mastery of the Will and the Way being significant. There were psionic as well as magic items. The difference was that psionics had a personal cost while magic had an external cost.
Don't get me wrong. In an earlier post I mentioned that psychic mutants is a trope that appears in lots of post apocalyptic stories - and Dark Sun takes inspiration from those stories (including psychic mutants). But honestly? The word is interchangeable. It's just magic by another name.
Similarly, I could replace Magic with Psionics in the PHB and basically nothing would change.
I think, "I'll just re-flavor psionics to not-psionics and now with not-psionics and the setting is unchanged therefore it doesn't need psionics," is completely missing the point of the question. If anything, I think it proves Dark Sun needs psionics. That it needs something to play the role that psionics plays in the story of the setting. That's like saying Star Wars doesn't need Han Solo because they could've hired anybody at Mos Eisley; or that Wrath of Khan didn't need to kill Spock because anybody could've gone into the engine room.
It just raises the question: Why not psionics?