Like most things in 2E, really great premise, dubious and fiddly execution.
This is exactly it. Some really good ideas, some incredibly bad execution.
Contrary to some of the silly claims early in this thread, 2E was perhaps the only edition which actually "got" how psionics/psychic powers could fit into D&D and do something interesting. It just had terrible early-2E style mechanics.
What I'd add was, again contrary to some early claims, is that D&D actually could hugely benefit from having two magic systems, because in fantasy fiction, there are, very broadly speaking, two common approaches to magic:
1) Magic is arbitrary, powerful, and can probably do literally anything. In these settings magic usually is "spells" which need to learned, and which usually bend reality in pretty wild ways, popping beings into existence, cursing people, summoning ultra-flames from supernal realms, making everyone forget a name (not talking about Peter Parker though it did happen there too lol), and so on. Often stuff is fire-and-forget, in that once a spell has been cast, it continues. Everything from a Wizard of Earthsea to Harry Potter to Jack Vance is basically in this very broad category. As is D&D's main magic system.
2) Magic is not that powerful, cannot shatter or even necessarily bend reality much (instead working with stuff like heat, atoms, the body's own systems, and so on), but is specific abilities to do specific things, which often overlap extremely heavily with what some settings are called "psychic powers". Usually there aren't "spells", rather
powers reliant on concentration, focus, willpower and practice/skill. There's no fire-and-forget here, generally - effects cease as soon as concentration is stopped.
Most fantasy settings have one or the other - trad fantasy, particularly that written by men, tends towards the former. However, fantasy written by women, particularly that which used to get labelled "romantic fantasy", is quite often the latter. Occasionally you have both - the obvious example is The Grishaverse (i.e. Shadow and Bone), where Grisha are generally using Type 2 magic (barring magical drugs and similar), but Type 1 magic does exist and is utterly terrifying. Arguably Robin Hobb's Assassin-verse also features both, though Type 2 is clearly the primary kind.
I think part of the reason D&D has so consistently shut out and misconceived mechanics has its roots in, sorry to say it, what is fundamentally sexism. I know some people will auto-bristle at that, but there we are. Male fantasy authors were
strongly preferred by the trad/medieval fantasy crowd until very recently, anyone trying to pretend otherwise has the vast evidence of discussions about Blue Rose to contend with (particularly those in the '00s). So whilst this second type of magic was always common as a proportion of fantasy fiction being sold, it wasn't the kind of fantasy fiction selling to people who made decisions about D&D, at least not until more recently. Even now I still very much doubt either of D&D's current lead designers are familiar with say, Bardugo or Hobb, despite them being huge-selling fantasy fiction authors (I think Mearls might have been - because the Mystic was very much in-line with a kind of upgunned Type 2 magic, but D&D's current leads seemed entirely perplexed by what makes psionics different from just "casting spells"), though I suspect the younger designers likely are.
Anyway, that explains why 3E fundamentally didn't get it - the designers just didn't understand that kind of fantasy, on a profound level.
4E was a lot closer to it, I note, and again, that suggests to me that Mearls (or others involved with 4E's psionics), despite any other failings, did "get it" re: psionics.