WayOfTheFourElements
Hero
I think it is a matter of the psion not being able to do anything -distinct-.
This is an issue all across 5e, of course, with some spells appearing on as many as 8 classes' spell lists, but I suppose the hope was that psions might escape that paradigm.
As it stands, any sorcerer can accomplish what a psion can...because there is no psion, per se; only a flavored sorcerer.
Look, if no one else in the party chooses any of the same powers, etc. it can feel distinct...but if an enchanter chooses some of the spells that do the exact same thing, it starts to feel like more of a pretense. Shrug.
Personally, I dislike the character building pre-game activity, nor do I find mechanical differentiation particularly compelling. I know a psionic sorcerer and an enchanter wizard will be nothing alike because my players aren't dullards.