The scenario I gave was what would have happened if the same three ships, which the Odyssey was destroyed by and the Defiant defeated by in their initial engagements, had gone up against a ship with the Defiant's ton for ton lethality, combined with the Galaxy's size. If the Defiant is a destroyer, this alternate Odyssey would be a battleship. And I actually scaled it back a bit, for a more illustrative story. More realistically, the Odyssey would simply fired its whole frontal weapons array, and those Jem'Hadar warships would have been debris.
If Starfleet was truly a military, they would have ships like that. But, they don't. Even the Defiant, which would have been the basis for an easy to build battle fleet, was mothballed until the Dominion emerged.
Given that the Sovereign was smaller than the Galaxy class but far deadlier, shows that while Starfleet still wasn't all in on building engines of war, they were a bit more aligned toward doing so.
The scenario you propose doesn't change much.
Ablative hull armor was a second layer of skin for the ship to help better protect critical systems.
There would have been no internal armor because the Defiant had none... the armor is mainly external.
Whether quantum torpedoes would have changed much... maybe... but again, the Odyssey has Sierra pattern attack which launches 6 photons simultaneously at a target.
This would have been the same as firing 3 Quantums (approximately).
However, the Dominion had a tactical advantage because they acquired technological knowledge of UFP technology in the first 2 years since the Wormhole opened.
If the Odyssey was more powerful, they would have probably sent more fighters to ensure the Odyssey's destruction.
At the time, the Dominion was one or two steps ahead of UFP because of their intelligence and were able to anticipate and prepare in advance for possible conflicts (small or large).
The Sovereign wasn't that much more deadlier or special than the Galaxy class. It just had more up to date systems in place (that would also be installed on the Galaxy class in the next maintenance cycle - bear in mind that the reason for the delayed system upgrade would likely be because Galaxy class ships are out exploring, so they'd need to return to a Starbase to be fitted with those new torpedoes and hull armour - though some upgrades such as the phaser and shield systems would be doable in the field itself).
The ENT-D was equipped with 260 photon torpedoes for crying out loud. It was implied to be a powerhouse of a starship when it launched with formidable weapons to boot.
Had SF continued with that kind of implementation on its exploratory ships and updated those systems regularly, its likely that the Galaxy would in effect be comparable to the Sovereign at the time of its launch, if not even more powerful (at which point, you assign different mission parameters to different designs).
But again, for the Dominion scenario, it doesn't change much at the time. The Dominion would have just sent 6 or 12 fighters to intercept the (hypothetically more powerful) Odyssey and make sure it was destroyed.