I don't recall psionics often having much 'hard science justification' in earlier SF literature -- or when they did, those stories where the exception, not the rule. It was more common to read about super-powerful aliens doling out Space Magic Crystals to Galactic Patrolmen so they can beat down the ferocious Mechanical Mind-Screens of the Yucky Tyrant Aliens (because, apparently, Space Axes can't cut through ferocious mind-screens).Over time, the original meaning of 'psionic' and its usage in providing a relatively hard science justification for the presence of seemingly magical effects was erroded in science fiction...
(Can you tell I've been reading E.E. "Doc" Smith's Lensmen saga recently?)
It's better to say that psionics date back to an earlier period in science fiction when the genre boundaries where much less defined, and mentalism, with or without technological augmentation, were par for the course. The idea that psionics in SF grew more 'magicky' is a nice sounding theory, but not a supported/supportable one.
(The only series I can think of right now which featured a reasonably plausible scientific explanation for telepathy is quite recent: Peter F. Hamilton's Night's Dawn trilogy.)
As for the original question: psionics = yay! A mishmash of genre elements is one of the defining qualities of D&D-style fantasy. I play D&D so I can pretend to be a elf who shoots a Mind-Slayer in the face with a bazooka I got on the other side of a Stargate!
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