As others have stated, his force was split and you could pound him with everything you had. I havent found fleet ambush to be beneficial for the ambusher yet, as it seems to always result in a situation like this. I like to take it as an objective in my list and hope that second player picks it. I have never seen anyone win who had to deploy part of their fleet in the box

The problem with FA is as long as first player has a split of large ships, fighters and small fast ships, his force will not be functionally split (physically yes, but we often spit our ships physically) by this mission, and if he's got good first strike such as a bomber list or big red dice arcs the second player may have just handed player one the victory with this mission pick, whereas missions should be sculpted to hand the second player the advantage. Just to put it perspective, as first player I would always pick FA unless there was a mission on offer for which my list had been particularly sculpted.

Yeah I just had this happen last night. Was playing against a 2 ISD 1 Interdictor list with a crazy bomber list. I chose FA and basically got to unload 9 tie bombers in range of 2 bomber commands on the first ISD he moved. It was limping right from round 1 and he never recovered. He never managed to catch half my fleet all the while slogging through a deadly cloud of tie bombers. Sure I lost 2 flots and a bomber but whoppteedo