I think you might have some of our names mixed up. The debate wasn't about whether all the cubes were the same size. There was the assertion that the tactical cubes in VOY were drastically smaller than all previously-seen cubes, thus excusing their apparent weakness. But this is nonsense because their original introduction was clearly meant to tell us they were more dangerous, and they were shown in fleets with the First Contact-type cubes, which devastated Starfleet's whole force, and were clearly the same size. I'm not sure what you mean by "quite a logical drawback". Does this mean "this is quite obviously a drawback" or "the Borg's uncreative nature is illogical"? Yes, the Feds' advantage definitely lies in their creativity and ability to think individually, but I don't buy that this means they would overshoot the Borg in technological advancement. The Borg can instantly assimilate any race's technology and integrate it with all the existing technology from every other race they have already assimilated. This would easily give them an edge over any single race's technology.