What happened with the superborg from "Before Dishonor" was a freak accident, something ridiculously improbable that won't happen again.
You are literally just making stuff up now. Nothing about that was a "freak accident." It was an adaptation that that cube developed and that, therefore, any other cube could potentially develop independently.
Indeed. As discussed on p. 100-101 of Before Dishonor
, the circumstances that led the cube to adapt in this way were unprecedented, but the adaptation was a choice
, not an accident. The technology of a Borg cube is sentient -- arguably more sentient than the drones, whose individual mental activity is suppressed. Starfleet's biases led them to assume that the deactivation of the Queen and the drones meant that the technology was inert, but that's not true. The Borg were as much technological as biological, and you don't defeat the Borg unless you defeat both halves. A thalaron weapon would neutralize the biological half of the Borg but leave the technology untouched, and that's not enough to make for a victory.
And what was the unique, unprecedented circumstance that made the supercube in BD choose to adapt in this way? In the Janeway Queen's own words, it was humiliated by its continued defeat at human hands. Probably a melodramatic way of describing their state of mind, but perhaps a more objective term is desperation. The mindset that drove the main Borg Collective to launch its full-scale assault on the Federation was similar: they'd gone beyond seeing the Federation as an annoyance and had recognized it as a serious threat. If the Federation had been able to use a weapon that neutralized all the Borg drones on over 4000 cubes, then it's not unreasonable to think that the surviving technological sentience of those cubes would experience the same sense of desperation, humiliation, whatever, and would make the same choice. After all, the incentive would be much the same.