Regardless of who or what is attacking or defending, the 'attacker' (and the guy scoring hits) is the guy who can outlaunch the other guy in terms of quantity and rate. There's also the matter of how fast one has to be to completely outpace the missiles altogether. Saying that, if the intention is to go up against even Galaxy-sized warships, then we're not talking 15 DF-fighters per, but hundreds per. That sized hull can pack in quite a few launchers and accompanying magazines. (And the D'deridex is even larger.) The ratio gets less when the enemy uses smaller warships, but there tend to be more of the smaller warships...
Tens of thousands of DF-fighters, soaking up tens if not hundreds of thousands of personnel, are built. On paper, that's impressive. In practice, not so much. They're doled out in groups that cannot support each other and in sizes that an enemy can take on with a mobile interstellar force. The enemy fleet can probably move around faster than you can shuffle around thousands of DF-fighters to worlds you think the enemy will attack. Or if you insist on ever greater quantities of DF-fighters to 'proof' each possible target, you're just draining even more resources and personnel from the thing that actually puts stress on the enemy: your own mobile interstellar force.
And a last thing to note, it seems that manpower is more of a problem for Starfleet than ships. Depending how you interpret it, that's what the big fuss after Wolf 359 was about. During the War, that was the opinion of Vreenak shortly before his assassination, though of course he could be wrong and Sisko couldn't very well comment on such things to a potential adversary.
Tens of thousands of DF-fighters, soaking up tens if not hundreds of thousands of personnel, are built. On paper, that's impressive. In practice, not so much. They're doled out in groups that cannot support each other and in sizes that an enemy can take on with a mobile interstellar force. The enemy fleet can probably move around faster than you can shuffle around thousands of DF-fighters to worlds you think the enemy will attack. Or if you insist on ever greater quantities of DF-fighters to 'proof' each possible target, you're just draining even more resources and personnel from the thing that actually puts stress on the enemy: your own mobile interstellar force.
And a last thing to note, it seems that manpower is more of a problem for Starfleet than ships. Depending how you interpret it, that's what the big fuss after Wolf 359 was about. During the War, that was the opinion of Vreenak shortly before his assassination, though of course he could be wrong and Sisko couldn't very well comment on such things to a potential adversary.