Yes, those would be the ones I would make transplanted humanoids. It would also highlight the fact that they're meant to be cultures as opposed to things that are genuinely ALIEN. It would help ground Star Trek in harder science and also make the setting more realistic despite my suspension of disbelief being quite high.
...It's not exactly something that Stargate created. It was also used on Farscape, Halo, and has it's origins in Star Trek: The Next Generation. According to current Trek canon, the entirety of the existing humanoid races in the Alpha (and probably other Quadrants) is that they were created by a predecessor race.
The flaw in your position is that you're using "human" and "humanoid" as interchangeable. You're blurring two very distinct science-fictional concepts: the concept that various human
oids, perhaps including the species
Homo sapiens (aka humans), are descended from a common ancestor originating somewhere in the universe; and the concept that all "humanoids" are actually descendants of
H. sapiens itself. Heck, those aren't just distinct, they're direct opposites when it comes to where humanity falls in the hierarchy.
Star Trek postulated the former;
Stargate essentially posited the latter (although it went back and forth -- originally the Ancients were posited to be a hominid race that evolved on Earth earlier than
H. sapiens but from the same evolutionary line, making them the first iteration of humans; but then they retconned them into immigrants from another galaxy).
As for why STAR TREK should do it. It's primarily a way of reclaiming what is owned by Star Trek to begin with, literary pedigree-wise. Star Trek influences and permeates virtually every science-fiction franchise in the world. Taking good ideas and putting a Trek spin on them is not demeaning itself because everything owes itself to Star Trek to begin with.
But I don't understand. If you're talking about Trek aliens being descended from a human
oid ancestor that is not specifically
H. sapiens, then
Star Trek has already done that, as you yourself point out.
It's not like humans naturally evolved on Earth in the Star Trek reality to begin with. According to TNG human evolution was affected. There's no reason to assume that all of human evolution wasn't the product of a race deliberately designing it to occur on a planet like Earths in a fashion identical to their own evolution in whatever universe they come from.
God, why even bring alternate universes into it? That's gratuitously overcomplicating the variables. It's a Rube Goldberg approach. Surely all of that can be justified (and already has been within ST) without tossing in totally random stuff about alternate or "earlier" universes. Our own universe is plenty complex enough.
Well if they evolved the Klingons, Romulans, and so on they've obviously been at work for literally hundreds of thousands of years. At the very least, they've been at work a million years in the past because that's when human evolution really got started.
You say "if," but what reason is there to believe that "if?" Why assume the Preservers are so all-fired powerful in the first damn place? All we actually know about them is that they moved a few Native American populations to another planet a few centuries ago, that they could build powerful repulsor beams and memory-wiping gizmos, and that they were so damn stupid that they thought it was a good idea to "preserve" these populations by sticking them on a planet that was routinely bombarded by asteroids. That doesn't strike me as a master race of great wisdom. There's no evidence that they have any technology significantly beyond the 24th-century Federation, and they seem to have a lot less common sense. And their one known operation took place no farther in our past than Picard's Federation is in our future, so there's zero reason to assume they're ancient.
I mean, even if you can postulate an ancient species that directed the evolution of all humanoid life (and don't we already have that in the Progenitors?), what reason is there to identify them with the Preservers? The Preservers had nothing in common with any of that.
More likely, they'd have to be there from the VERY BEGINNING and routinely effecting things to keep it all on track. So, the Preservers would be there for BILLIONS of years.
Typically a single nation or culture has a life expectancy of a few centuries, a few millennia at best. A typical species lives an average of two million years. And even within a single culture, policies and priorities can change on the span of decades or less. If a culture, or more realistically a government or faction within a culture, adopted a policy of preserving endangered populations or whatever, it might not last more than a few generations before priorities shift, or the original goals are forgotten or corrupted, or the government or organization that supported the effort collapses. Maybe, if a society is sufficiently long-lived and dedicated to the long view (like the European cultures that committed themselves to building cathedrals that took generations to complete), you could keep up a policy for a few thousand years. But billions of years? That's just failing to comprehend the sheer immensity of the timescale being discussed. Living beings and their societies are too dynamic to remain unchanged for anywhere near that long.