That may have just been a line flub that wasn't caught -- maybe he meant to say before they left Vulcan, or before they came to Romulus. Alternatively, maybe Narek is misinformed about Vulcan history. Maybe he buys into Romulan propaganda that they came first, or something. Just because a character says something doesn't require it to be absolute gospel -- especially when he's a liar in his own right and is a member of both a fanatical cult and an authoritarian government. Narek is anything but a reliable witness.
"Return to Tomorrow" did imply that Sargon's people might have seeded Vulcan when they settled space 500-600,000 years ago. But that's so far in prehistory that there's no way it would be remembered, or that a group like the Zhat Vash could've been in continuous existence. That doesn't fit with anything we know about the Vulcans' history.
No, they couldn't, any more than cavemen rode around on dinosaurs. They all date from totally different eras, and they did totally different things:
The First Humanoids from "The Chase" lived 4 billion years ago, before even single-celled life had evolved on Earth. They seeded the primordial soup of uninhabited worlds with DNA programmed to nudge their evolution toward the eventual production of more-or-less humanoid forms -- accounting for the existence of all humanoid aliens, even the more exotic ones.
Sargon's people, aka the Arretians, lived 5-600,000 years ago, or about 0.00015 times as long ago as the First Humanoids. Rather than seeding worlds with DNA, they directly colonized them with their own population, and may have been the ancestors of strongly humanoid species like Vulcans, and perhaps others like Deltans, Bajorans, Trill, Ocampa, etc.
As for the Preservers, their one known act could not possibly have happened more than about 4-500 years ago our time, or about 0.0008 times as long ago as Sargon's people or 0.0000001 times as long ago as the First Humanoids. After all, they rescued several endangered populations of Native Americans from different parts of North America (Spock said Delaware, Mohican, and Navajo, the third of which didn't emerge as a distinct group until the 1400s or so), which would not all have been simultaneously endangered until the era of European colonization. And all they did was relocate pre-existing populations to supposedly "safer" worlds (although the fact that they "preserved" the Native Americans by sticking them in the middle of an asteroid field with only one deflector unit makes them seem pretty incompetent). They were only meant to justify Earth-parallel cultures in particular (although most of the Earth-parallel cultures in TOS were given different explanations).
Personally, I suspect the Preservers are the same people as the Vians from "The Empath," since they had the exact same agenda. I'm surprised nobody else ever sees the similarity. It's because they're hung up on this false idea that the Preservers are some immeasurably ancient, long-lost civilization rather than just a few centuries old.
