Actually, the Sovereign appears to be exactly what Eaves described it: a long overdue replacement for the Excelsior class. It's more of a generalist workhorse like the old Constitution class and very much unlike the long-range fully loaded Galaxy.
That's pretty much what I consider the truth; additional tactical ability is just a reflection of recent advancements combined with the more hostile environment of the 2370s. I think it's more or less taken for granted that the Constitution
was quite well-armed for their day as well.
I imagine that the Galaxy
is capable of operating independently for much longer if need be, but that both the Galaxy
are generally capable of the same missions. It seemed that Excelsior
s were still being assigned missions similar to the Enterprise
-D in TNG, just with range limits in mind. The Sovereign
, being smaller in mass, would probably just have less of each facility that the Galaxy
"Jack of all trades, master of none" anyone?