I dont know much about the Babylon 5 universe but what is the primary doctrine of the Centauri?
I can't speak to Steve's campaign, but B5 is still one of my favorite all-time shows, even if the graphics are a bit dated. The Earth civil war was just such a great sequence!
In the show the Centauri Republic began as a fading empire, which had fallen from its days of greatness and retreated from its former conquests. It was only interested in keeping what it had and trying to ride on the coattails of up-and-coming races like the Earth Alliance. Even so they had a powerful navy, just not the will to use it. If I remember correctly, Earth Force, in the show, would have had a hard time fighting the Centauri Republic in a stand-up fight, as the Centauri had relatively advanced tech and the Earthers were relatively new. The difference was, the Earther's, being young and hungry, were willing to fight while the Centauri Republic was old and tired.
The Centauri's evolved during the run of the show, though, as did all of the races.