[AgentZero]

I don't think you'd need a whole fleet of Dreadnoughts if all you were going up against was Light Cruisers. During the Terran/Arkon-Tauran War, the Arkon Dreadnought Artemis fought off an assault force consisting of 230 Light Cruisers and 120 Destroyers and Frigates. Although, she was so heavily damaged after the battle that she had to be scrapped, and 90% of her crew were killed, but the point is that she did it!
For reference's sake, here's a pic of the Arkon DN with a LC flying alongside.