As it turns out, people are creatures who live on Athas too.I could get on board with that, (it also tracks nicely with the 4E idea of psionics as "nature's immune response to an unnatural presence") if psionic use wasn't so integrated into the populace as a whole and used so frequently in the city-states. Like if psionics was something of the "outside" (reinforcing the safer but subjugated aspect of the city-states versus the dangerous but free aspect of the wilds), and if you spent enough time out there, you might also develop those kinds of powers.
Not sure if I would call it "backdrop" when it's as ubiquitous in use as it is on Athas, as you even suggest earlier. I think that it reinforces that Athas feels alien and other, that other powers developed as a response to the dangers of arcane magic.I'd also like psionics better if that was the power being nurtured by the Veiled Alliance in opposition to the arcane power of the sorcerer-kings. I guess I'd just like it to be integrated into the thematic conflicts of the setting, somehow. To me, it feels like a sort of background story in the setting, and it isn't really reinforcing anything.