If you're getting swarmed by dreadnoughts, you're taking a really long time to spread out. I only saw them one at a time.
I just played through, first time. The last mission was a cake walk. You have enough resources in your corner area to support multiple cruiser production, and you have an anti-dread cruiser to work with as PHC, killing them is really easy. I was able to save Mac with about 50 logistics in mostly cruisers while I pushed left with a similar force around the time my first dread was coming online. It took Athena that long to take out the starting frigates. By the time I had to rescue him again, I could send him three Cronus fleets while I massed even more forces to take the lower left.