I imagine if you did a poll and asked fans of previous editions if 5e gave them all the options they wanted, you’d have an overwhelming number say no. And those would be fans of every edition.
OTOH, there's only so many things they want, and anything one wants that another doesn't can be provisioned as an option that the latter simply wouldn't opt into.
For instance, the other day I was lamenting how I missed how a lot of horrible things that could happened to your PC in 1e that weren’t HP related made the game feel different, and the overwhelming response was “good. Those sucked. No rational person would like those”.
But I don’t expect 5e to bring those elements in. If I want them, I either home brew, or play a different game. I’ve been doing that for almost 40 years. No biggie. That’s true of everyone, right?
It's not true of everything they might want, though.
5e has saving throws, it has spells, it has monsters, it has traps … it has everything you want except a consequence of some of those saves being non-hp based fatalities or other fairly final bad things. That's
very simple to implement, and you don't have to worry about balancing it, because, really, the point isn't balance in the first place, quite the opposite.
So, yeah, you're 95% there, going the last 5% yourself is no great hardship.
Building a whole new class, OTOH, let alone an alternate de-facto-magic-system, which is what a worthy implementation of psionics would presumably amount to, would be a major undertaking.
So major, professional designers apparently seem reticent to even try.
Sure, relative to the Big Tent pitched(npi) by Next, 5e's tent is failing - or, at least, being very slow to fully erect. Relative to the inflation-adjusted revenues of every other edition, it's succeeding. (Whether you take all the quasi-eds being published at once in 1983 as not being beaten out just yet, it's still a stunning success.)
I mean, how many times have I been told that the warlord exists in 5e, just under other classes?
It doesn't matter how many times you've been told something that isn't true.
Does that mean 5e failed me?
That's up to you. It's so far failed fans for whom lack of a warlord is, well, tautologically, perhaps, a point of failure.
Well, I'm not exactly thrilled that the warlord got thrown under the bus, but, I also recognize why it did - it was far to divisive to appear in 5e which was trying to appease as many folks as possible.
Uh-huh. That's kinda the point, really. 5e was pitched as being a solution to that division, that had to be done, because
nobody could be left behind!
Now that 5e is established, it turns out, plenty of folks can be left behind. Just not the folks who established their willingness to burn the hobby to ground with edition warring.
The fact that for the most part 5e is simply 4e mechanics reskinned means that it wasn't much of a jump from 4e to 5e.
I think you overstate that a bit. Yes, there's lots of mechanical and conceptual details that carried over. Yes, the difference between proficiency and 1/2 level is largely cosmetic, numbers puritanism instead of numbers porn.
And, the question isn't, "Are there fans of psionics" it's, "Are there enough fans of psionics to justify an entire sub-system catering specifically to psionic fans?"
And
optional sub-system?
Yes: at least one.
Besides, a whole setting, Darksun, effing runs on psionics.
And leaving them out of Eberron is short shrift, too.
We're the niche consumers and by insisting on very specific products, we've excused ourselves from the big tent.
RPGs
are a niche product.