The core set is definitely evenly balanced, but the opposing admirals have to use different strategies for victory. The strength of the Rebels is in their versatility while the Imperials excel at focusing on particular strengths. The Imperial player should endeavor to use his TIEs to destroy the Xwings. At that point, it will be much more difficult for the Rebels to successfully bring down the Victory within the round time limit. Things get far more interesting with missions, objectives and upgrades though.
PS. I don't think you will every be able to "bring her around" once the Rebels get into the aft or side arcs.