and how many ships have you lost?
and at which difficulty?
Admiral difficulty, I lost two CR90s, one Nebulon B, one Dreadnaught cruiser, and one Golan Is. I started with 3 CR90s, 2 DP20s, 4 Nebulon Bs, 3 Quasar Cruisers, 4 Dreadnaught and Cruisers, 3 Assault Frigates.
I started by going after Isard, since she offered a bonus. Hit her with the ion cannon, which dropped her shields down to like 10%, swarmed her with all my fighters and bombers,, ran away all my frigates all the way to the other end of the map. I ran my corvettes around to pick off enemy fighters coming after my shipyard and Golans. Once the Executors were engaged, damaged, and had their shields down, I brought my frigates back into the picture, maneuvering them around to the aft of the Executors, to finish them off.
The AI didn't seem to consider my frigates and fighters to be a real threat, because I expected it to retreat with at least the 2nd Executor once it was damaged enough. The AI didn't retreat even when Isard was almost dead, and didn't retreat even when the second Executor was down to a few hardpoints like they normally do when I engage them with capital ships. That might be some weird calculation the AI does to gauge the danger to its forces.
Hope this helps