The profile of the Sovereign class does resemble the Excelsior a bit. The Excelsior class despite several refits was very old by the 2370s so it is logical that Starfleet were thinking about retiring the Excelsiors and the Sovereign class does have some advantages over the Galaxy class in terms of being a flagship.
Aside from being a more modern design with newer technology compared to the Galaxy (which Galaxy refits could probably match with the correct upgrades) the Sovereign class is smaller, sleeker and more manouverable than the Galaxy class. Which would prove very useful in combat against the Borg as it would be harder to target the Sovereign class than the Galaxy class. Clearly it would be difficult to avoid incoming fire in a Galaxy class.