To be fair, the visual evidence for most of the CGI Galaxy-class starships would seem to indicate that the class generally underwent a refit of combat systems in the years leading up to the Dominion War. I imagine that it might have been more economical to continue production of Galaxy-class ships already being built as tensions were building up in the years prior to the war (modifying them during construction to be better combat vessels), and to have existing ships refit, than it would have been to ratchet up production of Sovereign-class vessels in the very few years they had between the class's launch and the outbreak of the war.
That's what what I always figured. I seem to recall something being said about the Galaxy being a modular design, and so having it be refit (or just redesigned in construction) from a lab-and-amenities-heavy science and exploration vessel that was extremely capable of defending itself (like the Enterprise-D) into an outright battlewagon struck me as perfectly in line with what we'd seen before.