I'd rather argue that the swinging of a sword or a fist is too close to certain vital non-attack functions that the Borg could ever completely block such an attack.
Guns they'll no doubt block easily enough (but only after the first two Drones have fallen to the attack, since the first two Drones always fall to an attack no matter what attack technique is used). The basic defensive technique would be simple: a standard shield, which is known to be quite effective against conventional explosions or ramming attacks. Just ramp up the power, and apply a bit of inertia control, and a Drone could quite plausibly become impervious to artillery shells.
But a slowly moving sword or a fist acts too much like, say, an object the Borg would wish to grab. They can't erect a forcefield against a fist because they need access to the fists of their victims for assimilation purposes. They can't put a tractor beam on a sword because they need to be able to manipulate slowly swinging metal levers, even sharply edged ones.
At least, that's how the requirements of drama would go. It would be too big a plot complication, not to mention too much of a tech contradiction, if the Borg could somehow block a swinging fist.