In any event, it's not surprising that he would get a ship similar to what he had before. Sisko helped design the Defiant and his crew was familiar with the vessel's systems.
And that brings about an interesting issue. Apparently, not everything our heroes did to their little ship was "public knowledge" - indeed, even the ambitious, unscrupulous and high-ranking Leyton could not dig up all of it in "Paradise Lost". And any ship built to the original Defiant
class blueprints would have been a lemon, supposedly, as per "The Search". So, was the Sao Paulo
better, worse or similar to the original?
O'Brien changed? Had he solved the original problems, or had he merely imposed flight envelope limitations so that the problems wouldn't manifest? Had he upgunned or downgunned the ship, upengined or downengined, tuned or detuned? Was the Sao Paulo
a series production model, or simply the last of the original, failed and thus expendable prototypes?