But take over what? Like I keep saying, the Federation isn't one place, it's hundreds of widely separated worlds. Evidence from canon and the literature suggests that, as per Anderson's portrayal, the interstellar civilization is so immense that it's something of a fiction to treat it as a singular, unified entity. The Federation isn't particularly localized either; it has arms and offshoots stretching far beyond its core territory and even beyond its neighbors' core territory. Sure, it's a stretch, but maybe the Borg could've gobbled up a set of colonies that were relatively close to their territory, close enough to trigger some threshold response even when the Borg weren't prepared to invade the core of the Federation. And then the Federation decided not to try any further colonization in that direction. Hence, "they assimilate entire worlds and we fall back." Hence Picard's talk of compromises and retreat.
And that's the problem. Ambiguity is important, because it allows flexibility and compromise and understanding. And ambiguity is far more commonly found in the universe than its absence. The more complex a system, even one as seemingly monovalued as the Borg, the more inevitable it becomes that it will have conflicting forces influencing its behavior, or that its behavior will be highly sensitive to initial conditions -- thus producing ambiguity.
And ambiguity is interesting. It's easy to make straightforward assumptions about how we expect the Borg to behave, but it's a lot more fun to imagine the possibilities that defy our expectations.
But we're here to have discussions, aren't we? So we should be open to finding new things to say. That's the whole reason I'm exploring this line of thought. The fact is, I consider your interpretation to be more plausible than the alternatives, all things considered. But it's also more obvious than the alternatives, so that makes the alternatives interesting. It's creatively challenging, and therefore fun, to try to figure out ways in which the alternatives could be true.
