I concur with Corbomite and Lt Q that the Galaxy-class is just a refit away from being a BB, and that the Federation is no stranger to war and its necessities, but rather than think they were "understating" it's role as a "politically correct" move, I think Starfleet has a different perspective than ours. How many times did Picard, Sisko & Janeway et.al. say in an episode that "Starfleet's mission is peaceful exploration." They are not a military in the way we think (at Roddenberry's insistence). Yes, they use a command managerial hierarchy, and they prove that when they have to, like with the Klingons or Dominion wars, they can arm up and slug it out when they have to, but I don't think they are "hiding" their ship strengths. Starfleet is "allowed" to build warships, they just don't, until something like the Borg comes along. The only issue, IIRC, about the Defiant was that it had a cloak, which was forbidden to the Federation under treaty, so Sisko wasn't supposed to use the cloak in the Alpha Quadrant (but he did anyway). I suppose in a way, that sort of treaty illustrates this idea - Starfleet was willing to go along with giving up cloak tech because they didn't want it; that is, until a rogue unit decided to build their own in secret anyway. (To retcon this, I think that the Pegasus and the phased cloak was a Section 31 action...)
It's worth noting, the "radio chatter" in ST:TMP at Epsilon 9 included a call to the "Dreadnaught Entante NCC-2120." So, there's seems to be DNs in Kirk's time at least.