Are you serious? We're talking game design here, not Orwell's essay on Newspeak.
Wizards used to be called Magic-Users (with wizard a level title). Rogues used to be called thieves (with rogue likewise a level title). High level MUs were called Mages and Archmages, high level druids Heirophants. Sorcerers and Warlocks used to be MU levels. Evokers used to be called Inovkers, and the school of Transmutation used to be called Alteration.
There's no general principle that requires identity in the naming of game elements.
Yay, ancient past and all, this is not the same. The level titles form 1e have nothing to do with the sorcerers and warlocks we know and love. From Magic-user to Wizard:Mage there is little difference, the mechanics remain pretty much the same between editions, the flavor remains unchanged as are the aesthetics, only the name changed. For 3e dropping the "Mage" part and leaving it at only Wizard is still fairly smooth and easy to identify -the biggest change was dropping all pretense of them encompassing all spellcasters under the sun-. On the other hand notice some of the 5e's translations of previous concepts:
Assassin -> Rogue: Assassin - same name, very similar mechanics, same flavour and aesthetics. I believe they are a good conversion of the 1e Assassin.
Warlord -> Fighter: Battlemaster - different name, different focus in mechanics, samish flavour but different aesthetics. No way it plays the same, not a cleric substitute, not making allies better, not being lazy, not being support. Kinda ticks only one out of four aspects.
Avenger -> Paladin: Oath of Vengenace - different name, similar mechanics, similar flavour but different aesthetics. Not sure if it plays the same, heavy armor and no manga weapons and all. Halfway between the previous two.
Favored Soul -> Sorcerer: Favored Soul - same name, similar mechanics (wings, heal if needed, spontaneous caster, lacks holy symbols, resistances, and signature weapon), same flavor same aesthetics. Not perfect conversion but a good one.
Now check Psion:
Different name - to make it more mainstream (so it is less sciencey, but what was wrong with psychic is beyond me)
Different mechanics - but similarish (what happened to the flexibility of psionics? all editions I know they are very flexible on the spot)
Different flavour - to make it more mainstream (not in your mind, you are channeling the far realm)
Different Aesthetics - to make it more mainstream (more hindu ascetic than psychic )
The only thing that makes me think they are supposed to represent the same stuff is the designers word for it. But on a larger scale the mystic of this UA and the psion of previous editions are as different as wizards and sorcerers on any edition with both. "Yeah 5e, has the psion, only it has a different name, story, flavor , shape and plays different yupy!"