@ Design Team: I actually think the Defiant is great as is, and considering I was guilty of the worst Defiant-Spamming in the first Entrenchment release, that should count for something, dammit! Seriously, you're right it's not 100% cannonical, nor 100% game-play optimized, but it fits a solid niche right now. I would not, however, be opposed to adding more cap ships, because, hey, they're fun!
@ Design Team (2): I'm going to start submitting abilities tonight (no, really this time)! Will start with torpedo laying, which has gotten solid, and evasive maneuvers (piece of cake, already done in my head), boarding party (pretty well figured out), and (my personal favorite) Glorious Sacrifice - which intend to be a klink cap ship ability to go on a suicide ramming mission when the ship's SP/HP are down to squat.
@ cperceful (can't resist setting you straight on some 'technical' Trek facts):
Just an extra note about science, the Defiant has performed science missions, despite science not being its role. Don't forget it was the first ship to ever open an artificial wormhole. The DS9 technical manual gives the Defiant's sensors at 80% of standard Starfleet sensors, which reflects its dedicated combat design
Um, not really on the wormhole - remember Star Trek: The Motion Picture? Granted, not stable and everyone wants to forget, but it was still earlier... 
@ Paradoxnt (more tech fun):
The Ship PowerPlant in the Galaxy takes up 12 decks.
The Ship PowerPlant in the Defiant takes up 3 decks.
Actually, according to the Galaxy Class tech manual, the deck size doesn't matter nearly so much as how well you can focus your matter/antimatter streams through the dilithium crystals to get your plasma stream. The Galaxy just provided a lot of verticle separation because the matter (deuterium) tank is near the top for refuelling and the antimatter (anti-deuterium) modules are near the bottom for ejection in case of an emergency, thus the greater number of total decks for the power plant.