Why are you assuming that only the Drones are the "processors"? I would assume the Borg have computers as well.

Based on the series and basics assumptions of the Borg, the total processing power comes from the Borg collective as a whole. From the references from Voyager, and TNG the terminals are subsystems to the whole collective. A singular drone cannot conceive of Unimatrix zero, nor does the Queen herself devise a plan to stop Janeway. Their computers are a subset of abilities in relation to the raw processing power of a Borg drone, otherwise the Queen and the Borg would have been attacking Voyager and Enterprise D/E with ruthless amounts of force to incorporate individuality and creativity. As such, the Borg would have been hyper aggressive in assimilating the creative powers of high ranking individuals instead of a total assimilation of the crew.

As for drones:

In Q-Who, the drone assimilates the schematics of the ship after the first drone dies. Drones are not there for the total assimilation of a species technology, only the minimum and maximum. It's very simple to create a model based on the specifications of the ship vs an individual chain of thought.

While 3 Quantum Torpedoes went in first, the whole fleet was needed to destroy the Cube.

As for First contact, I mistook a quantum torpedo spread as a singular torpedo. (its a been a while, and the synthohol has left my memory a teensy bit clouded)

If we take cannon as the total limits of starfleet, then the quantum torpedo was deployed for the first time against the Borg and matches my assumption of 1-3 hits of a new weapon to adapt. If this is the case, then one cube being targeted with the total knowledge of the Borg and an armada of ships makes sense for the Enterprise E to end it on the spot.

In general a cube learns the basics of the species and in the long term, such adaptations are expected through simulation as a direct result through the defined parameters of the hardware involved. As such, the Borg never compensate for individuality which leads to Seven of Nines improvements and Picard and Shelby's improvements and observations during TNG.

Hopefully this clears my line of reasoning, and if not, I'll be synthohol free tomorrow morning. :)