Why does everyone cite "The Chase", when the proliferation of humanoid species by The Preservers was already explained two decades earlier in "The Paradise Syndrome"?
In fact, it amazes me that "The Chase" even got past story development meetings. Did NOBODY on staff watch the original series?
That's a false equivalency. The Preservers don't explain humanoids in general; they were only meant to explain Earth-duplicate cultures found on other worlds, the sort of thing TOS did often to save money by reusing stored costumes and sets from historical films/shows. (Although most such duplications had other explanations -- interference in the case of the Iotians and Ekosians, deliberate imitation in the Platonians, etc.) The idea was that they took existing Earth cultures that they felt were endangered and transplanted them to other worlds. (Which means they may have been the Vians, who were doing the exact same thing in the Minara system.)
The First Humanoids in "The Chase" were meant to explain the much wider pattern of humanoid aliens in general -- why even heavy-makeup aliens like Klingons, Cardassians, and the like still had the same basic body plan and facial structure and were even interfertile. Lots of fans equate the First Humanoids with the Preservers, but that's ridiculous, since they're completely different in what they're meant to explain, what their methods were, and when they existed. The Preservers are a modern race, not an ancient one; their only confirmed act is transplanting Native American populations that wouldn't have recognizably existed or been endangered until about the early 18th century. If Moore said that a race living four billion years ago
was meant to be the same as the Preservers, then he had forgotten way, way too much about what the Preservers were -- or else had fallen into the cavemen-and-dinosaurs fallacy of assuming that everything in the past happened at the same time.
TOS also suggested in "Return to Tomorrow" that Sargon's people were the ancestors of most humanoids, or at least Vulcanoids -- but it was stated clearly that humans evolved independently on Earth, because for once a TV show's writers paid attention to their science advisors on that point.
In my mind, there's a clear division. The First Humanoids are responsible for the pervasive pattern of humanoid life in general, basically every species played by an actor in makeup. Sargon's people are the ancestors of more human-looking aliens like Vulcans, Bajorans, Betazoids, and Deltans. (I actually suggested in one of my novels that they included two distinct species, one humanoid and one Vulcanoid.) And the Preservers are a relatively modern group responsible for transplanting existing cultures to other worlds -- maybe not even a species so much as a nature preservation society, an interstellar Greenpeace sort of thing.