Was the first Mystic half-arsed or late in the edition?
No, that had an interestingly different set of problems, but basically was doomed from before it was ever published, because of WotC's self-imposed "70% approval" requirement for UA'd 5E content*. The Mystic also had some design issues, but the main thing was, it could have been literally the best-implemented psionics in D&D history, but it would never have hit 70% because more than 30% of D&D players who answer surveys either:
A) Just don't like psionics (for varied reasons).
or
B) See a UA as an opportunity to "hold out" for their preferred take on psionics.
(I confess to being in the latter category early on - though I liked the Mystic and just thought it needed paring down and about 3-5 powers needed serious nerfs/deletions - literally every "Mystic is OP" claim relied on exploiting those.)
How about the NEXT playtest rules -- late in the edition?
When were psionics in the NEXT playtest? I thought I had all the playtests that got publicly released and none of them have psionics in AFAIK. Am I missing one? Or was it in some private playtest? If it was private-era, that seemed to largely be paleo-D&D-players in terms of groups selected, and I doubt any psionics system would have met with even 50% approval from them, no matter how good. Can you PM it to me if it's from a private one? I'd love to see their early thinking. Further, even the open playtests, whilst interesting, were deeply unrepresentative of the audience 5E now has, being far more grog-y and WotC reacted to even them pretty strangely too - the more interesting Sorcerer design they had
seemed to be extremely popular (to judge by all the forum discussion), but they inexplicably ditched it favour of a much more 3E-esque approach. Anyway, the same point applies - if you make psionics part of a "popularity" contest, it gets ripped apart between the anti-psionics crowd and the people holding out for the precise version they want. The "hold out" group didn't realize this would result in "no version" I think - that's something new to 5E - in literally all other editions TSR/WotC just decided on a system, so no-one was initially afraid they wouldn't get psionics at all.
By the way, if you read my post carefully, you'd have seen I was implying that if, instead of going with a UA, they'd just published the Mystic (or preferably a cut-down version of it) as an official class back in 2017, it'd be popular by now. That's my point. Yeah, the "no psionics ever" crowd might dislike it, but there are plenty of people who ban plenty of "core" classes/races from their home games. But the large audience of newer players would likely have enjoyed it a lot, had they just been told "this is what's happening", I'd suggest (jmho ofc).
They've been trying to find a psionics system that people like from before the edition launched and then throughout. This is a poor claim.
No, you're not understanding the issue. You can't demand that a psionics system have 70% approval via a UA. Period. It won't happen. I very much doubt that 5E's spell-slot system (which is a big change from 3E and 2E and so on) would have even got 70% approval had it been presented as a UA. Certainly no existing full-caster class would have - they'd literally all be dismissed as "overpowered" or even "broken". Warlocks would be dismissed as "overcomplicated" and "unnecessary".
The only way to make a popular take on psionics is to come in early, and lay down a system you have faith in, then wait for players to see that it is good.
So spells-in-all-but-name? With a "manifestations" line instead of a "components" line? A whole mess of what's essentially reprints?
No. I don't know why you're saying this, but it doesn't follow from what I'm saying, and makes zero sense.
It's particularly bizarre because you then refer positively to the Mystic. A cut-down version of the Mystic is exactly the sort of thing I'm talking about. There's nothing "intricate" or "complex" about the Mystic, which is what people were claiming pro-psionics people wanted.
Sorcerer with subtle spell can cast every single one of their spells without V&S components. If you use the UA psionic-soul sorcerer, they can do that even easier.
No, they cannot. They'll run out of juice extremely quickly, and before they run out of spells (esp. when you remember cantrips exist). Why even say something that's obviously not true?
* = This whole "rule" is made a mockery of because if you have content that
isn't UA'd, no matter how junk it is, it can go in. They've even taken out UA/playtest content that was approved of, and replaced it with un-UA'd/un-playtested content (c.f. Marks in Eberron). So it's certainly no golden rule or something that has to be followed.