We have seen Sovereign in battle in all her movies so far, and I have never seen her dish out the punishment like the Galaxy class could. Small torpedo launchers that Sovereign has are there so that she can make up for the other small ones. She doesn't have anything like the massive 50 meter launchers that Galaxy has
The fact that she is the most advanced ship keeps her level with Galaxy, it doesn't give her a large advantage like some think, but sheer raw power of (War) Galaxy should be match for a Sovereign, whether she has families or not doesn't come into play.
We've never seen any Federation ship in the TNG era, except perhaps the Defiant, fight to their full potential. In many fleet battles in DS9 the Galaxy Class ships used their phasers most often.
Smaller does not equate to weaker. I will assume you mean the Galaxy has launchers that are 50 meters ( ≈164") long. There is no reason why the launchers on the belly of the Sovereign can't be 50 meters long. Also one could argue that the Sovereign has a better launcher design than the Galaxy, allowing the same fire power from a shorter launcher
Except for the Runabouts' "micro torpedoes', all photon casings look alike in size and shape. So it is a safe assumption that the Sovereign and Galaxy carry identical photon torpedoes. We've never seen the Sovereign fire multiple torpedoes at once (I.E. dispersal pattern sierra) but that doesnt mean it can't be done. Also if the launchers are capable of a rapid fire rate greater than the Galaxy that should close the gap with burst fire.
Most, if not all, descriptions of the Sovereign say her phasers are type XII (12), while a Galaxy is type X (10). Out of the box, the Sovereign has stronger phasers. Upgraded Galaxy's could have type XII phasers, nothing excludes that.
So, back to basics. Out of the box, the Sovereign is a stronger ship than the Galaxy. The upgraded Galaxy could equal the Sovereign in fire power, that assumes the Sovereign received no upgrades at all.
However, there is one bit of possible evidence that the Sovereign has been upgraded. Is First Contact
, she showed bubble shielding and in Nemesis
she showed the skin tight shielding seen in the battle scenes in DS9.