True. It means only that, except for the Defiant, Starfleet doesn't build them anymore.
didn't say that. Sisko just said the Defiant
was a warship, which is compatible with Starfleet building warships at that time, and having built them in the 22nd century, and planning on doing so in the 2380s as well.
Kira in response rolled her eyes and said "I thought Starfleet didn't believe in warships" - a quip Sisko didn't really deign to respond to. Instead, he held his mouth for a short beat, then moved on to explaining why the ship came to be - to confront the Borg.
Independent of that exchange, we don't know much about "Starfleet philosophy". Some skippers on some missions speak highly of the virtues of peace, but none really resort to non-aggression when an enemy tries to pick a fight. All our hero COs are seen conducting classic missions of military aggression, and (with the EXCEPTION of Sisko and the failed Defiant
!) all are confident that their hardware will carry them through. It would be easy enough to argue that Starfleet vessels are warships first and foremost, and that a certain percentage of them carry additional capabilities which are extensively used in propaganda to make people forget the basic nature of the Fleet's hardware.