Actually I would say it doesn't apply to Star Wars - that franchise's stock in trade is mysticism and destiny, especially in the post OT era. It's all presented as some kind of plan or fate, in which the characters are mere pieces to be moved, and the supernatural elements are explicitly portrayed as spiritual in nature. They don't 'play it straight' or claim rational explanations at all.
Okay, when you come right down to it, I basically agree with you on this (except that SW does mostly "play it straight" in dramatic terms, even when it offers no rational explanations), and moreover I'd say it's been that way right from the beginning of the OT. I mean, after all, it's a franchise that trucks in princesses and emperors and knights and swordfights. It has magic powers passed down by heredity, and a mystical Force that unites all reality, and cosmic archetypes of Light and Dark/Good and Evil. It's set in an ambiguous legendary past (long ago, far away), and the whole story is built around an isolated farmboy who has to discover his destiny by undergoing a Campbellian heroic journey. It's out-and-out fantasy, in other words, with only the most superficial trappings of SF (spaceships, ray guns, and robots, basically).
Still, in the popular consciousness, it's thought of as "sci-fi" and often compared to (or even confused with) Trek, even if only because of the word "star" in both names. So it's worth emphasizing the contrast. Trek is nothing like that.
...the law about 'advanced technology' hardly applies in the Vulcans' case - they are presented as entirely naturally occurring abilities. As for immortality, Sarek says they 'denied him his future' by not returning the katra to Vulcan before they even knew about the Genesis regeneration, implying some form of afterlife or ongoing existence of his soul.
I'll grant you, even though
STIII lampshaded what it was doing (with dialogue explicitly mentioning "Vulcan mysticism"), a lot of that film diverged pretty widely from the naturalistic traditions we're talking about here. (And arguably the film — and indeed Trek's whole concept of Vulcan culture — suffered for it.) I would never claim (nor does the OP) that past Trek has always lived up to those traditions flawlessly and without exception. However, I think it's fair to say that Trek at its best has consistently
tried to do so.
They do [call them gods] for the Prophets and Pah Wraiths, and Kirk (albeit somewhat facetiously) suggests classifying Trelane as a God. But then, to dissect the use of the term, what is a god if not a being of supernatural powers with the ability to create, destroy and alter at will, immortality, omnipotence, or whatever other powers you care to throw at them?
Trek has always presented the Federation as a free society where people can hold whatever beliefs they like, but that's different from saying anyone on DS9 ever took Bajoran religion
at face value. (Except for Kira, and it always seemed to me like an inexplicable deviation from everything else we knew about her character.) The Prophets and Pah-Wraiths were clearly just powerful inscrutable aliens, like many others. An actual god (at least in the Western conception) would have to be at least omnipotent, omniscient, and omnibenevolent, and even Q, arguably the most powerful entity in Trek canon, never met those criteria (frankly never even tried for the third). Q can have his powers taken away; we've seen it happen. We just don't understand the mechanisms involved.
...We may refuse the term, but we are really just renaming the same thing. ... So the assertion that Star Trek has been entirely rational and natural on these matters simply doesn't wash. Trek is a universe of gods and magic, it just pretends they are scientific.
Again, I wouldn't claim that Trek has ever been "entirely" rational about everything. But when it's true to its philosophical foundations, it at least tries to hold rationality up as a worthy ideal.
Semantics matter here. "Just renaming" things makes a difference. Powerful aliens, disembodied consciousnesses, and amazing powers are conceptually
different from gods, souls, and magic. It's an important distinction within the fictional universe, and it's also important in terms of how that fiction encourages people to think about the actual reality we live in.
(How much of what we do every day would be completely inexplicable to people of just three hundred years ago, for instance, and explained by them as "magic"? Yet we know it's not so, and they wouldn't be justified in calling it that.)
I think the OP is somewhat lost in the common belief among Trekkies that Star Trek is somehow scientifically legitimate for real, as opposed to pretending, and that Discovery is ruining that by going off piste. My main point is that Star Trek has never been scientifically legitimate in that manner, right from year one, episode one. So either we accept as you do and I do that science fiction is just about how the 'magic' is presented, or we accept that Star Trek has always been fantasy.
I think you're framing things in terms of a false dichotomy here. Fallacy of the excluded middle. I wouldn't claim (nor does the OP, nor anybody at all, really) that Trek is "hard SF" in any rigid sense. It's not "The Cold Equations" or
The Martian, not by a long shot. The Trek universe has certainly got more than its fair share of handwavium, unobtanium, and applied phlebotinum.
But despite all that, it's still definitely not fantasy in the sense that Star Wars is. How things are presented
matters. As the OP put it, when Trek was being true to its principles,
Society was what we made of it, not contingent on supernatural forces. Puzzles could be understood with observation/thought. Problems could be overcome or engineered, if society was wise and careful enough. Social issues could be solved with enough understanding. ... Everything that history tells us makes civilization good - reason, science, humane ethics, realism, the ability to forgive, or to exercise discipline - Star Trek was a partisan for.
Finally...
Discovery has gone out of its way to present the mycelial network as a scientific concept. It's ludicrous, and we all know that. But it still presents it as a natural phenomenon to be studied and harnessed, as a sci-fi show does, not a mystical or religious concept.
Maybe you should take a fresh look at the OP. USS Einstein wasn't objecting to the mycelial network
per se (although, I'll grant, others have). He(?) was objecting to the way it was used in that week's episode — as a mystical dreamlike reality in which Stamets could have a conversation with his dead boyfriend, without any pretense of a scientific explanation. That's noticeably out of keeping with its core function in the plot as a hyper-dimensional network connecting points in space.
The sequence is, perhaps, not enough by itself to set DSC apart categorically from past Trek series, not even TOS or TNG, never mind DS9. But it's an example of doing things wrong instead of doing them right when it comes to philosophical naturalism... of taking the show (at least a step or two) down a road it has no need to travel, one that leads away from what Trek at its best stands for. As such, it detracted from the story at least as much as it added to it. That's legitimately worth criticizing.