Well, I agree that it's weird to have a ship nearly as large as a starbase and the planets have always been too small, but the Titans were promised to be gigantic and have the ability to single-handedly turn the tides within a gravity well. All considering the description, I think this is about right. Yes, it would work better in a true scale game, but there are a lot of things done in Sins for the sake of mechanics, not reality.
Also keep in mind that they are in the very early development stages, when anything can be undone. They don't plan on testing for months. I believe they will either be late with the release or just on time, but pending a great deal of patches to balance out many issues they sidestepped to make the release date. Hell, Diplomacy itself has proven to be one giant Beta thus far with the newest patch.
