I struggled with this one a lot too. The key is to destroy the carrier as soon as possible, pretty much ignoring everything else. I did this by sending my fleet to the middle point with an assault order, with carrier rallied slightly behind. They are basically just there to draw fire while you close on his carrier. Keep shields down unless a torpedo strike needs to be blocked for maximum speed. Once you know where his carrier is, line it up and start launching torpedoes. They have a very long range so if you line it up well you can hit him from off screen. If he doesn't get his shields up in time 3 torpedoes can kill him outright. Once the carrier is down it's just cleanup. If you DON'T get the carrier down fast, the fighter/bomber swarm will just whittle you down after they destroy the rest of your fleet, which just can't stand up to the wasp drones.