We don't know what fleet Shelby was talking about exactly. Perhaps the fleet that is assigned to protect Earth was only 100 ships at the time, which this could then be considered as a devastating loss as nearly half of this fleet was lost in one engagement and would explain why the fleet would be back up to full strength by the end of the year.Robert Maxwell said:
One thing that always bugged me was the way the battle at Wolf 359 was considered a devastating loss, with 39(?) ships wasted. Several years later, losing a hundred ships sucks, but it's not the end of the world. It doesn't match up, and unless the Feds gathered a large number of allies with large fleets in the interim, or managed to build scores of large-scale replicators capable of making ships in a matter of days, it just doesn't make much sense.
Does anyone have an explanation for that?
Of course, you have the 'substantial reinforcements of 9 ships' line in DS9. How is that 'substantial'?
Not to mention The Way of the Warrior battle where under 20 ships is considered a good size fleet for Starfleet to have sent to DS9 to 'thwart off the Klingons'.
Once the war idea came up, they obviously thought about it in more realistic terms and realized that defending the Federation had to involve thousands of ships. Especially considering there are numerous hostile empires bordering the Federation. In order to be fully prepared for a war from either one, thousands of ships would be required to provide any sort of defense.
This is just like the 'speed of warp' debate.