I've never understood the obsession some people seem to have with making The Preservers some all powerfull godlike race, when there wasn't really much evidence for that in the episode they were introduced in. All we really knew about on the show is that they moved some people from one planet to another and set up the machine to protect the planet from asteroids, and neither of those really require technology much more advanced than what the Federation already has by the 23rd Century.
I've been saying that for ages. Not only that, but if their idea of "preserving" a population was to stick it in the middle of a dangerous asteroid field with only one defensive beam, that makes them seem pretty damn incompetent. (I mean, what if the asteroid comes in from the opposite side of the planet?)
Plus there's the tendency to assume that the Preservers had to be incredibly ancient, even though their transplantation of Native Americans requires them to be quite a recent civilization. The three tribes Spock mentions as their antecedents are from entirely different parts of the country, and the only time they would've all been endangered at once was after European colonization, the 17th or 18th century. Plus one of them, the Navajo, didn't really exist in a form Spock would've recognized prior to the 1600s.
While we're at it, why does everyone assume the barrier surrounds the
entire galaxy? All we know is that it exists locally, on the part of the edge that is reachable to the
Enterprise. And the Kelvans are the one and only extragalactic species we've ever known to be affected by it; there were plenty of other extragalactic entities that got into our galaxy just fine, like Sylvia & Korob, the Mudd androids' builders, the space amoeba, the "One of Our Planets is Missing" cloud creature, and the Nacene. So this notion that the barrier is some kind of impermeable shrink wrap around the entire galactic disk doesn't make any sense. The only reasonable depiction of the barrier I've ever seen is in
The Wounded Sky, which explains it as an ephemeral, local feature, the shock front of a massive extragalactic supernova or something of the sort.