If energy weapons are useless on the Borg after they've adapted, but Worf is still able to chop one up with his Mek'leth during "First Contact," why don't all the Federation troops just replicate some Samurai swords and go to town whenever the Borg attacks?
Well first if we discount the Borg updating their shields to stop swords (and I'm not suggesting they couldn't do this!)
And the if we discount them just shooting their attackers with energy weapons before they get close enough to use swords (which I don't see any reason we should!)
Then as soon as they start allowing themselves to get attacked by an enemy with swords they could start carrying swords of their own learn about swordsmanship from their attacker and soon become as good if not better than the attackers with swords
Worf is a very strong, experienced melee combatant with years of training with melee weapons. His weapon is heavier than a sword and seems to work almost by percussive smashing and piecing rather than slashing, however let us assume they replicate weapons which have the same physical characteristics for our humans.
Imagine what would happen if there was a dozen scared, almost panicing, completely untrained people swinging swords around in a confined area. It would be a nightmare of friendly fire (even without the Borg shooting at people).
I have fought on a re-enactment battlefield and had my face opened by a backswing on someone on my side and both of us had had years of training.
Even if the swords got through the Borg armour. It would have been hightly dangerous as close as that as one touch from a Borg means BIG trouble.
Worf is stronger (than most humans), better trained (at melee combat) and has his chosen weapon at hand - the humans will not be anywhere near as efficient.