Well maybe subtract about 500 for bombers lost, subtract 500 for reserve aircraft per squadron, and double the remaining number for number of pilots. The latter part is what's significant as well as logistics. Where are all those pilots going to sleep if you pile them into one system? You have to drag their respective destroyers from their Battlegroups to the area of ops.
And that means you more or less decapitate each Vasudan Fleet, since the destroyers form more or less the C3 for their fleet. It's simply unsustainable. However, this gives you a great advantage as you can rotate the squadrons fairly easily, so you don't have tired and battle weary pilots on the front line for over 30 days. You may have been able to supplement perhaps 3 squadrons at most to the 13th BG, but you definetely can't concentrate all those bombers in one place.
And then there's also the issue of escorting those bombers, and the Shivans aren't stupid. If they see that many bombers heading at them, they're going to call for help or perhaps run tail until they meet their friends. Then you're going to be in one helluva fight, think, fleet on fleet battle possibly. It's a delicate balancing act.