Hussar
Legend
What's wrong with associating mystics with swamis and gurus? Isn't that what a psion is? And, at least with mystic, my verdampt autocorrect doesn't keep kicking in and trying to change psion to poison. 
But, in any case, psionics is what a mystic uses. There's no real problem with that. We don't call a fighter a weaponist after all, even though that would likely be more accurate. We don't call casters magicists. Casters use magic (either divine or arcane). Heck, we dropped Magic User twenty or so years ago precisely because of this. Fighter types use weapons. Barbarians use Rage. Mystics use psionics.
Not naming the class after what it uses is pretty much in keeping with D&D naming practices.

But, in any case, psionics is what a mystic uses. There's no real problem with that. We don't call a fighter a weaponist after all, even though that would likely be more accurate. We don't call casters magicists. Casters use magic (either divine or arcane). Heck, we dropped Magic User twenty or so years ago precisely because of this. Fighter types use weapons. Barbarians use Rage. Mystics use psionics.
Not naming the class after what it uses is pretty much in keeping with D&D naming practices.