Umm, except we never saw evidence of modern superweapons in use, and yet Earth prevailed. Unless one counts a handful of quantum torpedoes fired by the E-E, or a volley or two from the pulse phasers of the Defiant, neither of which seemed to do much damage. The "heavy external damage" wrought on the Cube was apparently thanks to classic ships like Miranda, or classic weaponry aboard more modern ships like Nebula or Akira. And the decisive shots were thanks to conventional firepower under "insider" fire control from Locutus of No Longer Quite So Borg.
But she was a failed design. Her propulsive systems did not work: she nearly tore herself apart on trials. Her other assets did not appear decisive, as the pulse disruptors of a Bird of Prey could do the same job as her pulse phasers (remember the ambush in "Time to Stand"?), and the quantum torpedoes never featured much in the fight against the Dominion.
Why mass-produce a failed silver bullet when something like Saber, apparently with tried and true solutions, might be mass-produced in its stead, probably in greater numbers for the lower unit price?
They didn't bother with the Defiant, that's the point here. And there's no evidence that either Sovereign or Akira would be a post-Wolf 359 design, or that the Prometheus would be intended to fight the Borg, or be particularly good at it.
Timo Saloniemi
And you think the fleet that battled the Borg in FC did not undergo weapon upgrades ?
Hardly ... if they didn't, then the cube would have got to Earth with no damage whatsoever.
The anti-Borg technologies were supposed to be brought into service about 14 months after the initial Wolf 359 battle.
That gave SF more than enough time to bring those techs into service by upgrading existing ships and even further enhancing them prior to FC.
The heavy damage the cube suffered was thanks to the fleet, and once the Enterprise E arrived it helped deliver the crippling blow.
SF was working on a starship design which was intended to fight/defeat the Borg (the Defiant) and when the ship proved to be unstable (which was quite frankly expected) they gave up on it.
So why exactly did they keep her in 'cold storage' just so they can hand it to Sisko a year or two later ?
Sorry but O'Brien and DS9 crew in general were able to solve most of Defiant's issues in just a few days and then fully stabilized it shortly after their mission to the GQ to find the Founders was finished.
I'm guessing someone at R&D is slacking (seems to be a recurring theme actually because they gave up on just about any new thing that presented a challenge only to state an episode later how they don't give up just like that despite the issues).
Sisko clearly stated that the work on the Defiant was stopped because the Borg threat was not an immediate one (a rather lame/horribly stupid excuse) and not because SF thought that the ship was a failed design.
Ok ... so the Saber class was supposed to have been a tried and proved design, right ?
Then why didn't the Federation create some 300 of those ships, upgraded to the max and sent them to fight the Borg ?
No ... the writers messed things up (as usual) and portrayed how the top brass at SF got arrogant yet again (which is idiotic to begin with because they knew the Borg are a huge threat that can ensue at any time).
They could have resumed work on the Defiant, solved it's problems (since I highly doubt O'Brien is smarter than the whole SF engineering corps put together), and mass produce it so they can have them in readiness.
The Dominion War would have probably went better for the Federation if our side had even 100 Defiants on standby.
Heck, the only ship to undergo real upgrades was the Lakota.
And if SF did those kinds of upgrades for all ships, I think the War would have been a wee bit different.
But I guess drama was more important, while realistically speaking such a blunder would never happen.
To our knowledge the Sovereign, Akira and Prometheus (along with the Defiant) were ALL post Wolf 359 designs.
It's true we don't know weather or not the Sovereign, Akira or the Prometheus were intended to fight the Borg, but one would think that such a premise would be part of any new ship design that features decent amount of weapons and shields for protection.