This planet-that-cannot-be-like-Earth-but-is could be the work of the Preservers, or then merely something they made use of. Heaven knows the Trek galaxy is full of Earth flora, even if the fauna is a bit more diverse.
True, but I got the impression McCoy and Kirk were describing smells of well-known things (honeysuckles and orange blossoms), looking at "pine trees" and not as like this or similar to that, but that, "exactly," as some olfactory memories told them, and Spock, IIRC, was impressed since it would be astronomically against the odds to have exact copies, which isn't something he's ever said simply because they also had trees and/or flowers. The galaxy is filthy with those and that doesn't impress Spock as astronomically improbable. Now go one step further – The Preserves transplanted the humanoid species, so why not transplant the flora and fauna they were used to and upon which their entire culture depended, too? It seemed likely. In that case, though, I think they'd do the plants and insects first, then other animals, and finally the humanoids. It would take time - maybe a lot of time.
If the Preservers can terraform an inherently unsuitable planet, then they might create one where No Man Will Ever Go, just to keep their transplants secure. On the other hand, massively terraforming a planet might involve diverting hundreds of asteroids towards it for use as raw material - perhaps somebody powerful left such a process unfinished a few million years ago, and the best the weak Preservers could do was install the deflector?
I don't think they'd put a larger rock together, but use one Ma nature provided. They might move it, or alter it a bit, but significantly altering its mass is so far beyond us it might take more god-like beings than I expect The Preservers are, or a much higher level of dedicated industrial engineering on such a massive scale that I'd expect an entire Empire to be left behind that we could detect – like the Tkon Empire (but that died out 600,000 years ago, and the Preservers came after that to gather up Native Americans). So I believe they are a much smaller operation or organization - a bunch of galactic do-gooders who can, via superior advanced tech rather than sheer size and power – Terra form a bit, transplant some "worthy" species, as they travel about the galaxy. It might almost be a hobby, or a special department of a larger, galactic but nomadic people. That way they don't leave traces of huge, planet-based civilizations behind – only their craft – their handiwork – their gardening, so to speak. They might still be around and on the move, but thousands of years moved on along the galactic periphery by now. Their descendants might one day return and cross the same space their ancestors did, and it might be desirable to see what had grown since their people were last through there, but it could take millions of years to make one circuit around the galaxy. Or maybe they stay put, relatively speaking for reasons of dimensional convenience, and let the galaxy rotate under them once every 230 million years. They terraform planets and stellar systems that come to them, and flip them – ha ha – transplant worthy species on to them.
But if the people doing the transplanting are powerful enough to create the not-Earth, then they might also be the ones responsible for diverting the Moon-sized rocks, and we might be back to the "petty crime" square, with the Injuns kidnapped for use in mineral extraction once the deflector brought suitable rocks down to the cheap shirtsleeves working environment. It's just that entire Moons aren't prime targets for illegal mining by such means! Perhaps the last thing the criminals did before fleeing was diverting the Moon rock down the same path their smaller platinum asteroids had gone previously, now with the intent of destroying all the evidence?
Anyone that advanced would find manual labor by animals (even humanoid ones) relatively inefficient compared to robotic labor, IMO, so slave labor seems a daft reason to me – far less plausible than raw ingredients, anyway. And anything the size of our moon would likely be spherical. It would have to be stronger than steel straight through to hold a non spherical shape if it's that big. And mining in space is likely to be cheaper than mining on a larger planet (particularly if you need to take the material back into space). Only if the planet is big and hot and has cooked the minerals a long time to help concentrate them would mining on a planet be better, and that paradise planet wasn't like that (too new).
Also, I doubt the same asteroid keeps returning. Why would it? It must be a new one each time. And since the skies darken ahead of time, long before the asteroid could be doing that, I think the obelisk does that to warn the natives something is coming and it's time to push the button. It's not fully automated, however, since only if the natives are sill there to push the button is there a point to deflect any asteroids, and if the natives are gone or couldn't be bothered to remember the Preservers and their gift, then the asteroids will take a natural course since the unworthy species will have died out or proven themselves unworthy.
The sheer diversity of humanoid forms despite this programming might suggest that natural evolution reigns supreme - until this programming kicks in and randomly selects one species to elevate into humanoidhood. Or sometimes two or more if one doesn't pan out (or does pan out and leaves, like the Voth on Earth). But usually not at the same time, although there may be mishaps (Menk/Valakians).
Yes, there is a way to explain why other species besides humanoids evolve, too, despite the preprogrammed goal of humanoid, if you so choose to write that into the story and have already accepted the premise. My problem is all that code has to be not just hidden in the vast complexities of advanced life, but it is supposed to even be on the smallest single cell life form. And it has to be self-replicating, too. I don't think that's possible by any known means, and like the quantum nature of the universe, you can't get small enough to write that vast code in so small a space. Sometimes the problem is the very nature of the universe and not a lack of technology. If the Progenitors left hidden machines around to more actively tweak life as it evolved to more "interesting" stages, that would be more believable, but to hide the puzzle, the awareness of surrounding species on the planet, to select one and drive it toward humanoid form, the ability to alter the hardware of some random device like a tricorder, and play a complex hologram, all written and hidden on the simplest life form is, IMO, impossible and ridiculous. So unless one imagines using higher dimensions to hide this code on the atomic level, it seems sort of like writing on electrons and making those words self replicating or transferable to new electrons than enter the system, and I don't see this happening. So in two ways, this "science" fiction breaks the rules of science fiction - the science is wrong on evolution and possibly wrong on quantum mechanics. It's no science - it's more fantasy and magic. This is fine for fantasy, but I don't really like it in science fiction.
Essentially, sapient humanoids are just parasites feeding off this thing called life. And they need not be the end goal - the Ancients are apparently gone, but not necessarily dead, since several of their handiwork have further evolved into noncorporeal beings instead. That may be the ultimate goal, with our current status just a larval stage. Or then there's a lot beyond noncorporeal, too.
Humanoid form was THE goal of the progenitors. They, themselves, had not yet apparently achieved a non-corporeal form when they did this. If the universe tends to favor noncorporeal life, that would happen without that code's assistance. Now maybe the Progenitors did evolve to noncorporeal life, but if so, it was after, and we have no evidence of that, or even that they would any longer care about what's happening down here on the old corporeal level.
But even planting the puzzle so that it doesn't decay in the billenia takes much more than currently known science. Why not go the extra mile? It sounds eminently doable.
The graininess of the universe makes it sound undoable. And I suspect since we have code that can test if it was transmitted properly (I'm not the tech guy to ask about this, but they have redundant bits and means to know if it is corrupt) it's not too far to go to think the puzzle code, at least on that level, could reject the flaws. "Flaws" or mutations in copying are, of course, what drives evolution in the first place, but the self correcting puzzle code could be immune to that problem, and if one believes this premise, it's already not using mutations to drive the species toward humanoid form anyway.
Out of baselines as different as those of Anticans and Antedeans? It sounds so forced to me that I'm happy accepting it is forced!
But it could be "forced" by a means other than ancient genetic manipulation. Opposable thumbs are useful. So they, or something similarly useful, will be forced on the species if they survive and will become tool users. Other things in the universe might "naturally" favor the humanoid shape for advanced, tool using, scientific, space faring species, and not having something similar naturally makes it far less likely (not impossible but less probable) to arise as an intelligent space faring species.
....Larry Niven had it the other way around, although it wasn't spelled out in the Trek version of his universe: the Slavers seeded food all across the galaxy, and when they died and left all that food lying around, it ultimately evolved into humans!
Did it evolve in the Pak race, or despite Niven's common origins, were the Slavers and the Pan Protectors two separate creations of his, or in the same fictional universe but separated by a great deal of time?
...But is that bad, when we don't actually learn Earth would be special in that respect?
It's only bad if something similar isn't happening everywhere else, lest you explain how Earth is somehow magically different and special amongst all other planets, materials, stars, or whatever in this universe. But it demonstrates more fully writers lack sufficient depth to write alien "Shakespearian" quotes or have scientific discoveries attributed to other alien scientists. Sure, it's quite human centric and earth centric, but I would hope to see more "quotes" and "discoveries" from other non-Earth cultures and non human species in the Federation.
How could it not be, without some sort of a supreme interstellar power to stop all the meddling from happening? All it takes to have Olympian Gods is one corporate vacation gone awry. Time machines justly are not just all over the place but also all over the time as well. Trek is rife with means of travel, so travel happens a lot. And it probably happens a lot everywhere - do we really have a reason to think Greek or Roman myths are proprietary to Earth, or even to a single Earth-alien pairing?
I don't know about "supreme" power, but the prime directive or similar beliefs might help isolate more primitive cultures, and the time cops (or whatever those Fed boys are who have the temporal directive) would help curtail messing around with time streams. But before that, it would be hard to stop alien visitation and interference with more primitive cultures. We hear of some of those, but too few of those from other planets. But then we hear too little of other Federation planets as it is. You would just expect, all other things being equal, the Andorians to have similar possible stories of Greek-like-god-like visitors, etc., and maybe they do, but we don't get to hear about them enough, so it makes earth look more unusual than it probably should.
The key there is having enough time for the primitives to forget how they were influenced. If aliens dressed in togas came down on Peloponnesos mere three and a half thousand years ago, we'd still know which way their hair was parted. But if they came down twenty thousand years ago, and their diluted memory then became the Greece of 1.5k BC, we're talking borderline plausible.
I do wonder how long Apollo was sitting on his arse waiting for his children. Was it just a few thousand years since the Greek were worshiping them, or Tens of thousands and the Greeks we know of were worshiping their memories and the stories of even their ancient ancestors? I'd have taken the time to gather a few laurel leaves just to learn that much.