Angry gith and kalashtar noisesI have never understood what the interest in a "psion" is, nor even what a "psion" is. Nor do I feel that the people who desperately want a "psion" have ever been able to explain what one is to me adequately. So I totally sympathize with any designer who, attempting to create a "psion" finds that there is no coherent definition of what a "psion" is, how it adds to gameplay, or even how it is different than a sorcerer or wizard.
Fundamentally, "psionics" in D&D have never been defined by anything but variant mechanics. And really, not since 1e AD&D has that variation had a clear and compelling reason.
In 1e AD&D a "psionic" character was one that had innate magical talent that was largely independent of the level of the character. This concept of innate magical talent that a person was just born with was tied by flavor to the attempts of mystics to reconcile their beliefs in magic with rational world of science, and as such it used a lot of modern language to describe very old superstitions in an attempt to clothe them in pseudo-scientific language. Of course, D&D got the language wrong, as for example the word "psionic" is a cognate of the word "bionic" and is meant to refer to a machine that grants abilities to the mind - a concept we'd now mostly think of in the context of cyberpunk such as installing modems in the brain to allow mind/machine interfaces. Still, at least it had some sort of coherent concept that made it different that a "Magic User" and anyone of any class could be a "psion".
Furthermore, psionic powers were novel mechanically in that they used mana points rather than spell slots. This incidental detail would be basically the sole defining trait of psions for the next two iterations. Psions were basically sorcerers with a slightly different spell list but critically using mana points rather than spell slots. It was as janky as heck, and I don't think really anyone could explain in this period what psionics were. Often a rather large percentage of the text was devoted to discussing what psionics might be without ever reaching any sort of definitive solution. Where they magic? Where they not magic? If they weren't magic, what were they? No one really seemed to know but there seemed to be pretty wide recognition that different tables had adopted different explanations or more often non-explanations.
Most of the attraction that I observed seemed to be focused on the mechanical difference. Some people really hated spell slots and really like mana points, and that was that.
So as an amateur rulesmith, I have no envy for the job of any designer that is supposed to create 5e "psionics". I recognize that there is a ton of interest, but the fact that no implementation makes a majority happy is not at all surprising. In prior discussions about psionics, I've only been convinced that psionics were always a bad idea with questionable implementations, however much they excited the imagination of a few.