This is in the Red Corner's favor.
Enterprise D isn't especially good at combat but it's the closest thing there is to a Federation Battleship. The Defiant is a tough, strong little ship but I don't give it good odds against a well captained Galaxy class, and the Enterprise D has had various improvements and tinkering by Geordie over the show.
Couple that with the Voyager, thing has improvements by a !FUTURE! Borg, various other tinkering, it took on a god damned tactical Borg Cube at one point.
The Enterprise B might not survive the initial salvos at all, it's an older ship and up against the largest Federation ship and one of the most modern.
Quantum torpedoes range from 'basically photons' to 'ten times the power!' depending on the scene and film, Sisko's best chance is a full salvo of everything he has on the Enterprise D's bridge or warp chamber. Otherwise he's just going to get obliterated with a huge amount of phaser arrays.
Actually, as far as the GCS is concerned, it is consistently portrayed as being a powerful ship. It would be more accurate to say that the ship is not optimized for combat. We can see that in the design theory that obviously went into the GCS, the role of the GCS within the franchise, and the design information that we get from the technical manual.
Design theory, the TM and the show clearly indicates that the GCS was intent on being an explorer ship, complete with scientific and diplomatic facilities. Even more telling was that families were allowed onboard, complete with daycare and school facilities with children. There was even room set aside for a dolphin tank, referenced both in the TM and later as a one-off comment in the show.
Within the show, the GCS is consistently referred to as a capable starship. During the alternative setting where the Federation and the Klingons are at war, the GCS was indicated to be a capable warship with very few differences from what we saw in the prime timeline. It was also able to take on three warships long enough for the Enterprise C to return to its original point in the timeline, thus restoring it (Yesterday's Enterprise). The Duras Sisters were furious with the idea of trying to take on a Galaxy Class Starship until presented with a means of bypassing the Enterprise D's shield--at which point they were able to inflict heavy damage (ST: Generations).
Finally, looking at the TNG TM, we know that the Enterprise D's shield generators are indicated to be top-notch in the setting (TNG TM: Shields). We also know that the Enterprise D's photon torpedo launcher is burst ten (TNG TM: Weapons). The burst ten-launcher is devastatingly powerful for an alpha-strike and follow-up attacks would be about 4 torpedoes for a quick reload (TNG TM: Weapons). Very few ships in the setting can actually match that sort of firepower.
Here's the thing: a Galaxy-class from around when TNG ended was shown to be completely helpless when faced with three Dominion fighters not much larger than a runabout.
The Defiant-class starships are purpose-built warships. The others are not.
In regards to the Odyssey being destroyed by three Dominion Fighters. First, Dominion Fighters are more like gunboats than actual fighters, even if that's their operational role. Second, the Odyssey was not there to destroy the fighters as quickly as possible. Rather, the captain was no doubt trying to reduce the blowout of an interstellar incident against a great power that the Federation had little to no information about. Against an opponent who was a tactical unknown. On top of that, the phased polaron beams made that difficult. Even so, that wasn't enough to actually defeat the Odyssey. It had suffered some damage but was capable of limping back home. Nor did the three fighters force an attack upon the Odyssey. Rather, one was chosen to make a suicide run. The obvious message was the Dominion's resolve in defending what it perceived as its territory.
Finally, in regards to the Defiant, while its space is purely dedicated as a weapon's platform, you also need to look at what it's actually carrying. It has two forward quantum torpedo launchers, one after photon torpedo launcher, four forward pulse phaser banks, and one or two minor phaser banks here and there for overall cover. Even if we were to link those pulse phaser banks as being on-par with a Romulan Warbird's pulse disruptors (1 GW), the fact is that the Defiant simply lacks the firepower and range to compete with a GCS that is going all-out. The Defiant could probably inflict a bloody nose, but the GCS could just drop a burst of ten photon torpedoes and there's very little that the Defiant could actually do to survive. Even if it managed that, it would probably be too crippled to carry on the fight.
Even if we're generous and assume that the Defiant's quantum torpedoes manage to KO the GCS, it's a fight between an Excelsior class and an Intrepid class. For an upgraded Excelsior, that's probably an even fight, but the Intrepid has a more effective shield grid, more advanced sensors, greater maneuverability, more advanced torpedoes, and much faster computers. The advantage probably tips in favor the Intrepid, even if the Excelsior were fully upgraded.