I voted for Sorcerer subclass also, but I really very torn.
Psion's never were "high charisma arcanists". They were studious, disciplined, focused, and almost scientific in their development of Psionics.
So what would erase the issue for me would be a Sorcerer subclass that swapped Charisma for Intelligence. But basically mimicked the powers of the Wizard in this UA that was just released.
Either that or if this Wizard in the UA got rid of the spellbook and just had spells known instead. Hell, even made that psionic focus item they talk about act as your "spellbook"/dojre/Power Stone where you "mentally scribe" your new powers known, ala
Power Stones
That would work for me too.