According to Memory Alpha, Ronald D. Moore said back in the 1990s that he had considered but did not end up using the interpretation that the progenitor humanoids were the Preservers. He noted, however that
but this could be them and be internally consistent
There's no reasonable way that it could be true in the novelverse given what your novel The Buried Age
says that the Manraloth did, though, can there?
Well, it wasn't reasonable anyway. It makes no sense to expect a single species, let alone a single civilization, to survive for four billion years. That's just fundamentally failing to comprehend how big a billion is. (Okay, the Q are billions of years old, but they're presumably not corporeal, organic beings.)
Not to mention, again, that the two races have nothing whatsoever in common
aside from being excuses for humanoid aliens. One engineered biospheres on the genetic level, one simply transplanted existing cultures.
Not to mention that the Preservers simply aren't advanced
enough to be four billion years old. They didn't demonstrate any technological capability beyond what the 24th-century Federation has -- just space travel, powerful tractor beams, voice-activated locks, and memory-wiping rays. They were far from godlike.
The problem is that so little was established about them that there's an enormous void for people to fill in with their imaginations, and in circumstances like that, people tend to go to extremes with their imaginings. So the Preservers have been blown up into this mythic, ancient, nigh-divine cosmic force, when there's no actual basis to ascribe such qualities to them. For all we know, they were just a space Greenpeace, an organization rather than a species. Heck, I still think they were the Vians from "The Empath," who were doing the exact same thing