You can't really separate mechanics from story.
I agree, mechanics and narrative must "cohere".
A character cant pretend to be a flying creature if jumping off a cliff lacks the mechanics to fly.
Psions are basically superheroes.
I agree, especially in the sense that a superhero concept is likely to have powers/spells that thematically express the personality of the character concept.
Limited in scope of what any given one can do, but basically endless.
I agree, that at-will cantrips and spontaneous spellcasting, and using higher level slots to boost a spell, are important for both the Psion and the superhero.
The psion needs to be able to use their powers at will, with short rest augmentation.
Right now we need to understand better what designers are planning to do about short rests. They seem to be phasing out, while using proficiency times per day.
But in principle cantrips are important, as well as spell modifiers resembling Warlock invocations.
Iceman doesn't stop using cryokinesis because he used his ice slide too many times in a day.
Iceman has cold related cantrip. There are different thematic cold spells, that represents different kinds of stunts that he has mastered in routines, including a low altitude virtual flight.
Daily spells are a non-starter for me.
That is your preference. But consider 5e short rests may no longer exist. The 4e psionic classes actually rejected the encounter powers in favor of the daily powers.
In any case, long rest capabilities represent a maximum amount of energy that one can wield effectively. One can even use the DMG spell points to divide a high slot into two low slots, or merge two low slots into a high slot. This system has math that hurts the eyes but it is there as a concept.
A player can spend a daily slot on a spell with very long spell duration, thus continue to use it at will.
Most importantly, the game engine uses slots to measure and balance all effects.
Those that want that have the wizard/sorcerer already.
Flavor matters. Many of the necessary Psion mechanics are missing. Many of the Wizard mechanics are wrong and disruptive. I like less Sorcerer mechanics. Psionics is any mental ability.
No need to waste the 3 pages to have another pointless daily spell caster class. We have 4 too many of them as is.
This is when it becomes difficult to maintain sympathy for what you want.
You dont care about what other D&D psionic fans want?
So I remind you that what you want is not D&D.
