Yeah, you're misinterpreting things. It wasn't the full caster status that was poorly received.
Dude, you are in denial over what's happening here. Again:
"In 2017, we experimented with an unofficial character class—the mystic—focused on psionic powers..As much as many playtesters enjoyed the psionic themes in the mystic,
feedback was also clear that the class encroached on other classes’ territory and that it was often too complex, too powerful, or both.
Following that feedback, we’ve decided to say farewell to the mystic and explore other ways of giving players psi-themed powers, as we did with the features of the Great Old One warlock in the Player’s Handbook...
The philosophy of this approach is most akin to the one taken in the 1st edition of D&D, where
psionic powers weren’t the domain of any particular class but were available for characters of different types to experience."
Hello? Is this thing on? Are you listening? They have CHANGED THEIR PHILOSOPHICAL APPROACH TO PSIONIC CLASSES TO MAKE THEM NOT THE DOMAIN OF ANY PARTICULAR CLASS, SIMILAR TO THE 1E APPROACH.
That is where we are at. You don't have to like it. You don't have to agree with it. But you do have to accept that is in fact where we are at right not and not pretend we "have" to have a dedicated full caster Psion because that's the "established" fact. It isn't. It is, very clearly, not what is established right now.
If you're going to get a dedicated full caster Psion, your argument must be more persuasive than "it's established as that". Because if you don't, you will lose.