I think the only mistake done to the Borg by TNG was the introduction of the Queen.
However, Voyager managed to destroy it, along with a unimatrix 01 and all TW hubs in the galaxy.
Therefore, if the Borg survived, it's possible that they could perceive the queen as an error in their calculations and simply remove her from the equation (Humanity was more or less on the losing side of the conflict with the Queen out of the picture).
while I will agree that the destruction of the cube in BoBw resulted in a 'lucky hit', the rest of TNG didn't fare any better.
Same went for Voyager.
As for Voyager going up against the Tactical cube and surviving... case in point, Voyager was newer than a Galaxy class and could have sported some anti-borg systems SF made in the meantime, and let's not forget that it's offensive/defensive systems are likely identical to the Galaxy class -same power in a smaller package.
But if you also recall, this encounter with the Tactical cube happened AFTER the ships shields and weapons were enhanced by 'One' - granted, that Sphere was able to counteract voyager's phaser beam with a feedback pulse, but I would surmise that 7's presence on voyager countered numerous 'tricks' that the Borg could have done to them... along with SF engineers on the ship who had time to analyse the results of the combat and come up with a way to counter them.
Plus, phaser beams delivered to the Tactical cube at the time were short bursts... probably very powerful short bursts at the same time.