It was completely overhauled and reconfigured by both Captian Sisko (the Project's Designer) & Chief O'Brien allowing the ship to function optimally and retain it's overpowered edge without sacrificing stability of the class.
Alternately, O'Brien just installed some limiters so that the ship could never be run at full power and thus wouldn't rip herself apart. We do hear that the ship in the later seasons still has serious problems with high warp speed, requiring trickery to go past warp nine where other TNG era vessels have maintained such speeds with relative ease.
I assume this because, the Project wasn't just to design one ship and validate it's effectiveness, it was to design a class of ships that could be mass produced, cheaply and efficiently (Think the Ford Model-T) packing more offensive power than any other ship of its size and tonnage.
This is possible. However, it is equally possible that the ship was an expensive "silver bullet" and that only two prototype hulls were ever built, these being the
Defiant and the similarly registered
Valiant. Perhaps mass production of these vessels was particularly difficult, being more comparable to the smallish F-117 bomber than the smallish Model T automobile?
Some people take Sisko's "The Search" comment about this design being the first step in building a battlefleet against the Borg and interpret it as meaning that Starfleet intended to build a fleet of
Defiants. But it could just as well be that Starfleet used the
Defiant to test concepts that would allow it to later build "real" warships, not ones hobbled as badly as this undersized testbed that was unsuited for mass production.
Sure, the
Defiant class later grew in numbers, something that no other known starship design did during the war. But the growth wasn't particularly massive: two or at most three ships of this class per each multi-hundred fleet seen... So perhaps the idea of silver bullets would better fit the description than the Model T idea does?
It's also possible that the Registry #s were all Legacy #s from previous "Famous" or "Battle-Tested" ships that had been decommissioned already but their Names preserved to pass on their "Record of Accomplishments". Similar to the Enterprise.
Possible, I guess. But when Starfleet has recycled numbers previously, it has used a letter suffix to denote this trick. There is no direct indication of registry recycling beyond the letter-suffixed
Enterprises and arguably the
Yamato.
Timo Saloniemi