Regarding the Defiant...
It was fighting the cube for the entire length of the battle. The voices over the speaker on the bridge of the Enterprise, you can clearly hear Worf there. By the time the Enterprise got there, a lot of ships were already destroyed, including the admiral's. The cube was already pretty well beat up, too. The other ships, we have no idea if they were there from the start or if they arrived later in the fight, but the Defiant was definitely there from the first shot. Considering it was the only Defiant class ship around at the time (and Sisko saying it was supposed to be the 'first of a battle fleet' before the project was scrapped), I'd say she did remarkably well.
AND... she did survive the cube blowing up, even after being crippled like she was. Something at least 1 or 2 other functional Starfleet ships couldn't do as they were trying to outrun the explosion.
Tough little ship, indeed.