I need to stop editing my post while you're writing the response to it.
Bigger is irrelevant. The Defiant is much smaller and better in combat than either. The Enterprise D is big because it's optimized for research and diplomatic missions. It's larger size gives it a lot more surface area to protect, a lot more mass to drag around the maneuver. It's a bigger target. More photon torpedoes and more phaser banks, I have no way to confirm whether or not that's correct, but again quantity is not an argument of quality.