We are never given a pure taste of the strength of Dominion Battleships and Battlecruisers, in every episode we only see their "puny" attack ships. The Dominion battleship certainly had no trouble obliterating a Defiant class ship, one of the Federation's premier warships. We are only given "twice the size of a Galaxy and three times as powerful." So we have no evidence. Not to mention the massively large Planetary Defenders in What You Leave Behind (again... an ambiguous debate) that if the scaling is correct, would be larger or about the size of a Borg Cube.
And people still seem to forget that if the Prophets didn't close off the wormhole, the Dominion's empire would have overrun the Alpha Quadrant easily. They had 2800 ships waiting to come through the wormhole to slaugther the Federations 627 in SOA, which from what we know is two large complete fleets of only a possible dozen or so Klingon / Federation task forces (fleet 10 was the highest ever mentioned). And that could be just the first wave of Dominion reinforcements... I doubt the Dominion would commit 100% of their military on a single assault.