Say, I hadn't made that connection. That works for me. Perhaps the Preservers are long gone, but they still have various bits of tech, like the asteroid deflector and automated spacebourne probes (which are really more like automated roaming starships) doing their dirty work. Perhaps a probe like the whale probe would have eventually swung in to check on Miramanee's people. In that regard, it might be easy to lump the Doomsday Machine in with them, too.
See, this is my problem with fan theories about the Preservers: the idea that they're some long-lost ancient race. Judging from the way Miramanee's people were portrayed, they were probably taken in the 18th century or so, just a few hundred years ago. In the grand cosmic scheme of things, the Preservers are a
contemporary civilization, not an ancient one. People have far too much of a tendency to treat the recent past as indistinguishable from the ancient past.
If you ask me, the best candidates for the Preservers are the Vians from "The Empath." They have exactly the same MO: relocating endangered populations to new planets. True, Spock didn't recognize their technology as matching that of the Preserver obelisk, but it had been a few centuries. If you compared a 22nd-century phase pistol to a 24th-century phaser, it wouldn't be obvious that they were products of the same technology.
Alternatively, I'm not convinced that "the Preservers" refers to a specific or entire civilization. It sounds more like an organization, one that might have members from multiple species/cultures. Heck, since we only have one canonical piece of evidence of their existence, they could've simply been a short-lived group or faction within a single society.