The thing is, the Borg would still adapt no matter WHAT weapon you're using. If you suddenly switch to slugthrowers in the middle of the fight, then the next wave of drones that comes after you are the ones with thick armor plating and heavy kinetic barriers that your bullets can't easily penetrate. In that case you either switch to phasers and hope the reinforced drones can't shake that off too, or you find a NEW way to kill them and wait for them to adapt again. Or, if you have the misfortune of being in TNG, your only option is to [tech] your phaser's [tech] so that it's effective again.
Equipping your anti-Borg SWAT team with a wide range of weapons would be sensible if the Borg really sacrificed two drones to learn about each new weapon. Alas, our heroes can't put their trust on that. In "Q Who?", the Borg did not sacrifice several decks in their Cube to photon torpedoes like they did to phasers: they came "pre-adapted" to torpedoes and shrugged them off from the very start. So our heroes would have to bring out a smorgasbord of only the most exotic and attractive weapons in their arsenal to keep the Borg sacrificing their Drones. Which would be to the advantage of the Collective, not the Federation... Timo Saloniemi
^ Then you're still killing them one at a time, which will never work. I repeat: the advantage of the Borg isn't their ability to adapt, it's their ability to continue attacking -- possibly even DEFEAT you -- no matter how much damage you do to them. With anyone else, there's a possibility for "critical damage" where you can knock out a few major systems that'll render the entire system either inoperable or at least unable to fight back. The Borg don't have this problem: you can blow up their entire ship, and the two largest chunks of its debris will still chase you around, shooting at you. If you get lucky and reduce the entire vessel to scrap, the DRONES can still salvage parts from the debris and build another one from scratch. Overall, if you somehow manage to overwhelm a Borg cube and destroy it, you have to COMPLETELY destroy it, or else the last remaining pieces of it will regenerate and two weeks later it's coming after you again even stronger than before.
I'm not sure the Borg have ever demonstrated the ability to fight with fragments of a ship, or even with a seriously damaged ship. A swarm of Cubes will probably operate like a swarm of Drones, with individual units taking great risks because even their destruction will be to the advantage of the Collective. But individual ships have been disabled and negated as threats in many episodes, starting with "Q Who?", until time-consuming repairs could be effected - and extensive damage has resulted in infinitely long repair times, such as with "Unity". As for the Borg sustaining an attack until the opponent is subdued, it's something we only hear spoken of. Our onscreen heroes have never quite had to face that yet - except perhaps in the long, strategic term. What rather happens to them is that they conduct a strike against a defensive Borg force, and attain their limited tactical goals even though the Borg defenses are not significantly weakened for the loss of half a dozen Drones or some Cube systems. When the aims are limited, a limited spectrum of "surprise" weapons is a valid way to attain them. Timo Saloniemi
"Our projections indicate that a Borg ship could continue to function effectively even if seventy eight percent of it was inoperable."
...Which is fine and well, but said "functioning" in practice seems to consist of staying idle and waiting for Picard to make a move. Why do the Borg waste time unless it is because of necessarily ongoing repairs? Timo Saloniemi
Adding to this point, the Borg Collective is a logistically massive entity. As such, if the Collective want you assimilated its just a matter of resources and time. They send one cube, you waste it. They send 10 cubes, you miraculously waste them all with version 2.0 of your doomsday weapon. They all die,but before you have time to build a commemorative statue the Collective sends 50 cubes to your doorstep-and all of them have adapted to your technology and defenses. Game Over.
Picard gets a +20 to his Attack and +10 to his Defense whenever he gets near the Borg. I don't think he should be mentioned in these discussions anymore.