Including that Dominion Super Battleship, I've noticed that the Federation has been lagging behind in ship size. The Klingon Neghvar, Romulan D'Deridex, Borg Cubes, Son'a Battlecruisers, Reman Scimitar and others are far larger then even a Galaxy Class starship. Now, I know that size is not necessarily equal to technical superiority, but it does have other advantages such as psychlogical. Seeing a huge ship can inspire fear and/or respect for one. Also, combat capability aside, very large ships can house all kinds of scientific laboratories, recreational facilities, shuttlebays, diplomatic quarters, sickbay trama centers, raw supplies, and so on. For ships that are far from any Starbase, perhaps years at a time if necessary, physical size can be a factor in its survivabilty and capability as an explorer, diplomatic representative, colony evacuation platform, etc.
What I'm getting at is, larger vessels have room to do more. Picture a Federation vessel larger than a multipurpose ship like the Galaxy Class, such as the noncanon Excalibur Mark I and Mark II or the Titan from ussmiranda.com. These vessels are much bigger than any in the current canon Federation fleet..