I agree it's a retcon, but I think it's one that doesn't create too much "damage." IMHO, I think the TNG crew accessing a transwarp tunnel in the Lore/Borg episode is harder to explain given what VOY showed about the tech then the assimilation retcon.
If you mean "Threshold"'s version of transwarp, VGR's own writers disavowed that episode as apocryphal and went on later to portray the Borg using transwarp conduits basically the same as the ones they used in TNG. But in any case, "transwarp" has been used to refer to several drive systems with apparently different modes of operation, some (mainly the Borg's) using conduits or corridors, others (
Excelsior's and the Voth's) not using them. So I take "transwarp" to be a generic term for any faster-than-warp propulsion system.
It was never said that babies were born as drones, just that the crew found an assimilated infant and made some speculations. That scene works perfectly well with later episodes where all drones were assimilated.
That scene might, but "Descent" does not, since all of the drones liberated from Hugh's cube were shown to have no prior identity or personality to recover, which is why they were so susceptible to Lore's cult-leader manipulation, which gave them something to fill the void. It's implausible that every single one of those thousands of drones on the same cube was assimilated in infancy. It only makes sense if they were conceived as Borg from the get-go.
And as I've said before, it's illogical to think that the Borg
wouldn't gestate new drones in vitro. They're all about efficiency, and it would be far too inefficient to waste the gametes their assimilated drones have to offer. Not to mention that gestating new drones from other drones' gametes would be a far more reliable and consistent source of new drones than the hit-or-miss process of searching for suitable populations to assimilate. There is simply no plausible reason why they wouldn't grow their own.
Thing is with the whole "non-assimilated drones" theory that Bennett put together for his books, at least the reason I don't really "buy" it, is that the Borg's assimilation aspect was introduced in their second appearance and was the keystone ever since.
No, it was not. It was introduced in BOBW as something the Borg did to
cultures collectively, since the Borg at the time barely even acknowledged the existence of individuals, and targeting a specific individual like Picard for assimilation was explicitly portrayed as an unexpected change. Subsequently, all drones we saw in TNG, in "I, Borg" and "Descent," were portrayed as pure Borg with no prior identity, with no suggestion that they might have been assimilated from previous lives. They talked about assimilating the Federation, but there was no indication that the specific drones we saw were assimilated. It wasn't until FC that we saw assimilation being practiced heavily, and that was implicitly because only a few Borg made it to the ship and needed to replenish their numbers. It wasn't until VGR that writers started assuming that
all drones were assimilated.
And as I've pointed out before, there is no reason to make this an either-or question. It makes sense that the Borg would use
both methods -- first it would assimilate a new population, then those assimilated drones would have their gametes harvested and used to breed or clone new generations of drones from that genetic stock. After all, it would be a terrible waste of material to let an entire assimilated species die out after a single generation. How stupid would that be? What's the point of bringing in new "biological distinctiveness" if it never lasts longer than a single generation and constantly has to be replaced? The
only way assimilation makes sense at all is if assimilated species are, in fact, reproduced within the Collective so that their biological distinctiveness
remains assimilated over the centuries or millennia. There's no point in acquiring livestock if you don't breed it. That's simply not sustainable.