I'm not interested in getting into a tedious debate about the merits of ship classes and particular commanders. But in a pinch, quantity has a quality all its own. If a hundred Defiants can be fielded for the same resources invested in one Galaxy, I think the larger number would be preferable in a war, especially if they can "fight above their weight class".
Well, of course it would make sense to field 100 Defiants VS 1 Galaxy. Maybe even if it were 10 Defiants to 1 Galaxy, which is far more realistic. But that isn't what I was talking about.
At any rate, production of both types of ships is important and shouldn't be relegated to either\or. Each is designed for specific missions. Defiant classes would be best used as recon or supply convoy and battle group escorts while larger ships like Galaxy and Sovereign classes as main battle ships in battle groups.