No implication at all, they have explicated that any implementation of Psionics will be transparent with magic, full stop. Yes, a full Psion Class would be a caster. That's just how 5E is built.
All editions had spells and "that's the way they were built", but that didn't stop them from creating alternative systems.
I'm going to need a game example of what constitutes "Psionics is in essence". Because my experience (3.5 and forward), is that Psionics has always been casting spells.
The 3.5 Psionic Powers were really just spells with different lingo. Psychometabolism instead of Transmutation, Displays instead of verbal/somatic/etc components, etc. There was even a clear X Power Points = Yth Level Spell. One can argue that the augment system is what lead to 5e having spells scale when cast using higher level spell slots.
In 4e, all powers used similar structure, though the augmentable at-will structure of the Psionic classes set them apart, it was still just like spells.
Even the Mystic can have their disciplines expressed as a collection of spells. Here, Mind Storm, one of the abilities from the Psychic Disruption Discipline, reformatted as a spell:
There, that's what I refer to. Of course behind the scenes everything can be a spell, even a Fighter's Maneuver, or a Monk's Ki Ability, anything. The point is exactly making it different. And not just for the sake of it.
Psionics in essence is a power that is much more fluid than magic. Magic is some kind of unlocking of the cosmos' secrets, so it works on its own rules. This is why Vancian magic doesn't break immersion even if it's such an artificial and arbitrary system: it's magic so you don't have to understand HOW it works, it's enough to know how to use it.
With psionics, instead, the users are unlocking their own power, and the rules are kind of their own, but they follow the limitations of the mind.
Hence every power should be flexible enough to feel like two or thee spells, depending on how it's used, how much effort is spent etc. Not just scaling damage depending on level like spells.
BUT they should all be thematically linked, because the mind has its limits.
That's why Disciplines are a cool Psionic concept: it's like you choose many spells in one, but all linked.
Psions should be very restricted in the amount of different things they can do, when they choose their powers. Like a skill-tree thing. If you are good at telekinesis, you can't just one day become good also at telepathy. It should be a gradual thing. If at first level you go for telekinesis, you would be opening some doors and nearly closing others. Retraining could be there as an option, but it would take multiple levels of retraining to fully change path. It has to feel more realistic than magic.
It's like superpowers: you know what to expect from superheroes, they have a set of powers and then they can use them in variations or at various degrees of power, but you don't expect Spiderman to communicate telepathically, or Professor X to shoot fireballs. While you expect almost anything from Dr. Strange, BECAUSE MAGIC.
There, this is psionics in essence, and although you could say it's just one way to see it, I'm pretty sure it's very close to all the other ways of seeing it, while Vancian magic isn't.
dnd.wizards.com
