The sound effects were mostly of the Enterprise-D being pummeled and taking damage, not of it firing back a lot.
And I fairly doubt that Soran was able to upgrade the BoP extensively.
Granted, he would be able to construct shielding for the trilithium torpedo so it doesn't burn up as it approaches the star ... then again, even with those enhancements to the BoP (provided they were done to begin with), the ship shouldn't have held out as long as it did in battle.
The crew also acted in a very idiotic fashion. Geordi was held captive by the klingon sisters for some time and the crew knew of their deceitful tactics.
Why didn't they bother to check the visor if it's been tampered with?
Also, rotating shield modulations very fast even with Geordi looking at them would likely not allow every shot to go through the shields.
Again, as for the Galaxy class production being suspended ... I don't think it would happen.
Sure that SF wouldn't really build as many as before right after the war so they can first replace existing losses with smaller/powerful ships of the new era.
I never said the Defiant is a match for the Galaxy class. I said it has an impressive fire power packed into a very small design compared to the Galaxy class.
Then again, Defiant was able to destroy a Jem'Hadaar bug with several shots, while the Galaxy class that fought a same design in an episode before, didn't do any real damage firing it's supposedly much more powerful phaser beams, and was actually blown up with a suicide run from the bug it was trying to dispatch.
There's a reason Defiant was designated a 'warship' after all. It would likely present a real threat to the Galaxy class (as it did to numerous Cardassian 'warships' ... poor as they are).
Whether or not it would win in a matchout, I don't know. Probably not, but victory isn't always dependant on who has a bigger ship.
I'd personally use Defiants and Saber class ships for border patrols that are close to star-bases and various space installations while sending larger ships more often to exploratory assignments.
SF ships can operate in a number of fields despite their designs. Of course that specific designs will excel better in one area or the other, depending on class (they'll be more efficient), while the Sovereign, Galaxy, Intrepid and Nebula, seem to be 'jack of all trades' type of ships.